T 1096/08 11-10-2011

Summary of Facts and Submissions

I. The appeal lies from the decision of the Opposition Division dated 23 January 2008 and posted on 7 April 2008 to revoke the European patent No. 1 127 209 pursuant to Article 101(2) EPC. In particular, the Opposition Division held that the subject-matter of claim 1 as granted did not meet the requirements of inventive step in the light of an alleged prior use presented by the Respondent (Opponent). The Opposition Division found that, based on a late filed affidavit, the prior use had been proved beyond doubt.

II. The Appellant filed a notice of Appeal on 29 May 2008, paying the appeal fee on the same day. The statement of grounds of appeal was submitted on 27 June 2008.

III. A communication pursuant to Article 15(1) RPBA was issued together with a summons to attend oral proceedings. The Board considered that it was appropriate to hear the evidence of Mr. Sjöholm and Mr. Peltonen as to the facts and circumstances of alleged sales of tube bits, and a decision for the taking of evidence from witnesses was issued. The oral proceedings were duly held on 24 November 2010. After the taking of evidence from both witnesses, the matter was discussed with the parties, and, at the end of the first oral proceedings, the appeal proceedings were ordered to be continued in writing. A further communication pursuant to Article 15(1) RPBA was issued, following a summons to attend further oral proceedings, which were duly held on 11 October 2011. At the end of the second oral proceedings, the Respondent withdrew all its then existing auxiliary requests.

IV. The Appellant requested that the decision under appeal be set aside and the patent be maintained as granted.

The Respondent requested that the appeal be dismissed.

V. The wording of claim 1 as granted reads as follows:

"1. A conical thread coupling for a drill string for percussive rock drilling comprising a male thread (5) and a female thread (4) cooperating therewith, said male thread being arranged on a first drill string element (3) and said female thread being arranged on a second drill string element (2), that said first drill string element (3) has a first impact surface (6) and that said second drill string element (2) has a second impact surface (7), said first and second impact surfaces being arranged to abut against each other, c h a r a c t e r i z e d in that the crests (8) of said threads (5, 4) have a radius of curvature which is larger than 30% of the pitch of the thread."

VI. The following matters and evidence have been considered for the purposes of the present decision:

VI.1 Alleged prior use "Robit Rocktools LTD/

Alwima Oy/Miranet Oy".

As filed with Respondent's notice of opposition:

D1 = Drawing of ring bit RR77,

dated 25 September 1992;

D2 = Brochure Robit Rocktools Ltd.

(no publication date);

D3 = Invoice 981236 Robit Rocktools Ltd.,

dated 13 May 1998;

D4 = Invoice 981272 Robit Rocktools Ltd.,

dated 2 June 1998;

D5 = Certificate Miranet Oy of 16 February 2005

(Mr. Peltonen affidavit);

D6 = Drawing of drill rod Terra-Team Oy 6847kk

(not dated);

As filed after expiry of the opposition period (with Respondent's letter of 22 November 2007):

D11 = Affidavit Mr. Sjöholm of 21 November 2007;

D12 = The original pencil sketch of 25 September 1992, corresponding to drawing D1;

As filed with Respondent's reply to the grounds of appeal:

D12a = Manual from SANDVIK Rock Tools, apparently published in 1994 ("D12" has been renumbered "D12a" by the Board);

As filed with Respondent's letter of 19 October 2009:

D17 = ISO 10208; first edition, 15 February 1991;

D18 = Robit ROCKTOOLS (web page), "released" on 7 July 2009 and apparently printed out on 31 August 2009;

D19 = Atlas Copco, Guide to product codes (no publication date);

As filed with Appellant's letter of 23 March 2010:

Annex 1 = Photograph of a typical copy lath, apparently taken on 23 February 2010;

Annex 2 = Photograph of a master or template

used with such a copy lathe, apparently taken on 23 February 2010;

During the first oral proceedings, held on 24 November 2010:

D21 = Three sheets of drawings/calculations, as filed by the Appellant (not dated);

D24 = Evidence taken of Mr. Sjöholm; transcript of the verbatim recording, pages 1/45 to 45/45, as attached to the minutes of the first oral proceedings before the Board;

D25 = Evidence taken of Mr. Peltonen; transcript of the verbatim recording, pages 1/17 to 17/17, as attached to the minutes of the first oral proceedings before the Board;

As filed during the second oral proceedings, held on 11 October 2011:

D26 = DE 1 170 887 B, filed by the Respondent;

D28 = Extracts from Sandvik Product Catalogue HR-12281-ENG 1997, filed by the Respondent;

VI.2 Alleged prior use "Robit Rocktools LTD/

Terra-Team Oy".

As filed with Respondent's notice of opposition:

D1 = Drawing of ring bit RR77,

dated 25 September 1992;

D6 = Drawing of drill rod Terra-Team Oy 6847kk

(not dated);

D7 = Drawing of drill rod Terra-Team Oy 7857kk

(not dated);

D8 = Statement Terra-Team Oy of 17 February 2005

(Mr. Vennola statement);

D9 = Invoice 13931 Terra-Team Oy,

dated 9 January 1997;

D10 = Invoice 14017 Terra-Team Oy,

dated 15 January 1997;

As filed with Respondent's reply to the grounds of appeal:

D13 = drawing of alleged fitting between D1's drill bit and the drill rod of D6 (not dated);

Offer of Mr. Vennola as a witness;

VI.3 alleged prior use "Robit Rocktools LTD/

Helake company/Terra-Team Oy".

As filed with Respondent's notice of opposition:

D1, and D6 to D10 (cf. point VI.2 of this decision

above)

As filed with Respondent's letter of 9 September 2011:

D21a = The picture of a tube, allegedly used with D1's ring bit and related to the "Helake company", not dated ("D21" has been renumbered "D21a" by the Board);

D22a = Product list, allegedly related to the "Helake company", not dated ("D22" has been renumbered "D22a" by the Board);

D23 = Translation of D22a, not dated;

Offer of Mr. Rajalin as a witness;

VI.4 Further Evidence:

As filed with Respondent's reply to the grounds of appeal:

D14 = GB 2 321 073 A;

D15 = EP 053 789 B;

D16 = US 4,968,968;

D20 = US 3,933,210 (cited in the patent and numbered "D20" by the Board)

As filed with Respondent's letter of 30 August 2011

D22 = Expert opinion ("Stellungnahme") Prof. Ulbrich, dated 18. August 2011;

As filed during the second oral proceedings, held on 11 October 2011:

D27 = Sheet 4/4 from US patent No. 6,196,598, filed by the Appellant;

VII. The parties submitted the following arguments:

VII.1 Alleged prior use "Robit Rocktools LTD/

Alwima Oy/Miranet Oy"

(a) Respondent's case

(a.1) The Respondent said in the written appeal procedure that it did not find any errors in the Opposition Division's reasoning and conclusion that the drilling bits according to the drawing of D1 had "beyond any reasonable doubt" become available to the public through prior use by the act of selling, as was evidenced by documents D3, D4 and affidavit D11. As far as the relevance of D11 was concerned, its relevance could not be denied on the basis that the author of this document (Mr. Sjöholm) had not been heard as a witness. It was the Appellant itself who requested during the oral proceedings before the Opposition Division (cf. minutes) that Mr. Sjöholm was not to be considered as a witness and should not be permitted to add anything to his affidavit. However, Mr. Sjöholm was now offered as a witness in order to clarify any remaining issues concerning the prior use.

Moreover, the logical chain of documents D1, D3, D4 and affidavit D11 was further supported by brochure D2 and certificate D5, the latter being signed by Mr. Peltonen, whose name had been mentioned as a reference on the invoices D3 and D4. Although Mr. Peltonen's statement should be credible as such, he was also offered to be heard as a witness to confirm the content of D5.

(a.2) During the first oral proceedings before the Board, the Respondent further argued that the witnesses had confirmed the existence of a single, unchanged product R77/49 of Robit Rocktools Ltd, which had been produced by Robit Rocktools in the relevant period of the sales D3 and D4 to Alwima Oy by Miranet Oy's salesman Mr. Peltonen, and was also described in Robit Rocktools' sales catalogue D2 of ring bits for overburden drilling equipment.

The customer (Alwima) initially provided the key-element, that is, the already existing drilling tube, whereupon Robit Rocktools used its threaded ending as a copy-lathe master for machining threads of the corresponding bits which the customer was asking for.

The Robit Rocktools' ring bit RR77/49 shown in D1 was not a manufacturing drawing used to determine precise dimensions for machining, but rather, a product-drawing in the form of a hand-made sketch to record the dimensions of the product machined by use of a copy-lathe. However, Mr. Sjöholm stated that the dimensions of the (conical) double-start rope threads of the bit documented by the drawing D1 in 1992 were taken from produced RR77/49 bits, ie the drawing simply matched the product. This was possibly the way the draftsman of D1 had done it.

As to the dimensions indicated on the drawing, Mr Sjöholm confirmed that the slight difference between the ring bit's outer diameter of 78 mm and the nominal diameter of 77 mm was common practice in industry. Such differences were even hinted at in the manufacturers' catalogues: cf. also D12a. Moreover, both witnesses agreed in that the ring bit rope thread usually had a pitch of half an inch, and since D1 concerned a double-start "RR" thread, the pitch was one inch, which corresponded to the 25 mm shown in the drawing. However, if the designer had made a machining drawing, the exact figure for the measurement would of course have been 25.4 mm.

To conclude, although the shape of the threads of Robit Rocktools' RR77/49 ring bit drawn in 1992 derived from an existing tube provided by customers, there was evidence from both witnesses that such ring bits, after they had been delivered by Robin Rocktools, always fitted onto the tubes of the customer's drilling equipment. The same applied in the case of Alwima in 1998. D1's ring bit thus corresponded to the prior sales of drill bits RR77/49 in D3 and D4. The calculations of the crest radius based on D6 and the Appellant's D21 had to be rejected, since they could not be understood and where therefore probably incorrect.

(a.3) The differences between overburden and percussive rock drilling newly addressed in the second oral proceedings resulted in a significant change of the case. However, the argument that the ring bit according to D1 had only been used for overburden drilling was technically incorrect since, according to Mr. Sjöholm, the drill bit was drilled up to half a meter into the rock: cf. D24, page 20/45. In doing so, the (drilling) system was fixed into the rock: cf. D24, page 19/45.

Contrary to the Appellant's view, there was no information whatsoever on file that for rock drilling it was required to drill several metres into the rock, the ring bit had to be (easily) uncoupled, or that the maximum drilling diameter was limited.

Moreover, particularly in 1998, no distinction had been made between rock drilling and overburden drilling. In case of percussive rock drilling, the broken material was simply removed by flushing. Reference was finally made to D28 of 1997. From the drawings on page 81 of D28 it was immediately apparent that at the time ring bits were used in equipment for pneumatic hammers, ie for percussive rock drilling. Patent document D26 gave background information on the purpose of the conicity of D1's threads. Thus, based on D1 and the witnesses' testimonies, the suitability and also the use of D1's ring bit for percussive rock drilling was disclosed to the skilled person.

(b) Appellant's case:

(b.1) The Appellant submitted that, contrary to practice as well established by case law, the Opposition Division in its provisional opinion had suggested in detail the wording of an affidavit. This wording was reflected in the subsequently filed D11. Quite apart from that, the Appellant had contested ever since, with reasons, the alleged facts in the affidavit D11 and, unless its author, Mr. Sjöholm, was offered as a witness, this evidence had to be ignored. As to certificate D5, Mr. Peltonen did not explain which of D2's products he had sold, or to whom. Certainly, he did not make reference to D3 or D4. Neither had it been explained how Mr. Peltonen was able to say that D2's products had the same conical thread as depicted in D1.

(b.2) When assessing the evidence of the witnesses taken during the first oral proceedings before the Board, the Appellant further argued that the thread profile RR77/49 was wholly derived from the master or drill tube. However, there was nothing on file relating to the copy-lathe, ie the master or the actual tube or their threads. Remarkably, every company in this field had had such rope threads on its drilling tubes as from the 1990s, but there was no evidence on file as to what their thread profiles actually looked like.

As to D1, this was not prior art in itself, but simply a sketch, that is, a brief summary of the tube's thread, from the profile of which it was copied. In particular, the figure "R8" Radius on D1 appeared to consist of two different circles, and since the draftsman was not available, there was no evidence as to what had actually been drawn, and thus changes could have been made to D1 at any time. Mr. Sjöholm had seen the sketch D1 in around 1993 and, therefore, he was being asked as to what was on the drawing seventeen years previously. However, even if the crest's radius of curvature "R8" indicated on D1 had to be read as figure "8", it was unclear how this radius of 8 mm had been derived from the tube or master, how the radius measurement had been carried out, and how the conicity (one percent) of the shown thread had been established.

Finally, the tolerances of the depicted dimensions were unknown. Assuming that the crest radius of the thread was really 8 mm, according to ISO standards for normal rope threads (cf. D17) the tolerance was still ± 0.4 mm. The radius of curvature therefore could have varied between 8.4 and 7.6 mm, and 7.6 mm would result in a ratio of crest radius to thread pitch close to 30%, ie outside the subject-matter of claim 1 of the patent in suit. The maximum allowed value for the radius of the crests could also be based on D6, which gave more information on the profile. However, in the light of D21, D6 disclosed a ratio well below 30%.

Thus, without knowledge of the actual profile on the master or tube which had been transferred onto the drill bit, it was impossible to say what had been delivered by Robit Rocktools to Alwima. Consequently, it had not been established to the required standard of proof "what" exactly was made available to the public.

(b.3) During the second oral proceedings, the Appellant further argued that, according to Mr. Sjöholm, at the time Alwima made geological drillings the delivered ring bits of Robit Rocktools were used for the purpose of overburden drilling through soil. In order to obtain a (geological) rock sample, a diamond bit was then introduced to drill (through the ring bit) a drilling core of solid rock: cf. D24, page 18/45 and 19/45. Although the overburden ring bit would enter the rock to secure the casing in the rock face, this bit was neither suitable nor used for (percussive) rock drilling. Mr. Sjöholm even stated that, technically speaking, "overburden" meant loose ground, and "rock" meant solid rock, which of course was harder and hence required a different type of bit: cf. D24, page 3/45 and 4/45.

Overburden ring bits have a substantial diameter for drilling through loose material until the rock face is reached. To prevent loose material from falling into the hole, a lining is introduced in the borehole. By comparison, percussive rock drilling is used to create holes in rock, for which purpose as much percussive energy as possible is transmitted to the bit. Moreover, to withstand the greater forces, percussive drill elements have a far smaller diameter, the maximum diameter being about 38 mm. Furthermore, the larger the diameter of a thread, the smaller the pitch angle for each revolution (constant pitch), and the tighter the drill elements are coupled together. As to D1's ring bit, the skirts of D1's hollow element were clearly too thin and its 78 mm diameter too large to withstand the forces applied during percussive rock drilling. The pitch angle shown in D1 is very small, which would made it impossible to uncouple such a bit from a drill string used in percussive rock drilling. Finally, neither the drawing D1 nor the witnesses gave any information on the conicity of D1's thread profile, and due to the absence of a male member it is very unclear what might constitute an impact surface on D1's ring bit to transfer the percussive forces. The selection of pages from catalogue D28 were not relevant, since the pilot bit shown there performs the percussive rock drilling and it is impossible to apply or transmit percussive forces to the surrounding ring bit and its tube. Therefore D28, which was late filed, should not be considered. Finally, D26 had been filed far too late.

Therefore, based on the evidence on file, D1 did not disclose a ring bit suitable for percussive rock drilling, let alone a ring bit which had been used for percussive rock drilling by Alwima before the priority date of the patent.

VII.2 Alleged prior use "Robit Rocktools LTD/

Terra-Team Oy"

(a) In its reply to the grounds of appeal, the Respondent argued that a yet further proof of public prior use of the drill bit according to drawing D1 was disclosed in D6, and D8 to D10, wherein the delivery dates of D6's drill rod together with D1's (ring) bit were indicated (via an invoice) in D9 and D10. As illustrated by (the drawing of) the enclosed D13, the drill bit D1 indeed fitted onto the drill rod D6. The threads of D1's drill bit were manufactured by use of a copy-lathe from the drill rods, and thus always resulted in an appropriate fitting. In practice, a template was first manufactured from the rod threads. The purpose of the statement of Mr. Vennola (D8) was to clarify how drawing D6 and invoices D9/D10 related to each other and how the drill bit D1 and the drill rod of D6 had been dimensioned to fit together. Further, the author of D8, Mr. Vennola, was offered as a witness.

During the oral proceedings before the Board, the Respondent emphasised that the further prior use (based on D6, and D8 to D10) was relevant and also had to be examined, since the evidence for it was filed within the opposition period. Although the Opposition Division did not need to use it for its finding, it did not consider it irrelevant.

(b) The Appellant submitted that although the Respondent argued that the threads of the male part on the drill rod D6 were used as the guiding template for the drill bit depicted in D1, this was certainly not what was stated in D8. The fact was that D6 was silent as to the profile of the threads on the male part. The thread on the male part had a pitch of 25.4 mm/turn, which actually did not correspond to that of D1, in which the thread had a pitch of 25.0 mm. Curiously, the drill bit illustrated in D13 was indicated as having a thread pitch of 25.4 mm, but that drill bit was not in accordance with D1.

Since the only information concerning the thread profiles of D6 related to the pitch, it was impossible to determine whether the crests of the thread had a radius of curvature which was larger than 30% of the thread, and thus a prior use of the claimed conical thread coupling had not been established. It was therefore irrelevant that Terra-Team Oy might have sold a number of these drill rods to the Research Center of Geology in Finland. In its reply to the Notice of Opposition of 9 June 2005, the Appellant however argued that it could not be proven by the invoices D9 and D10 that the products according to D6 and D7 (not to mention D1) actually were available to the public.

VII.3 Alleged prior use "Robit Rocktools LTD/

Helake company/ Terra-Team Oy"

(a) The Respondent submitted that D21a showed a picture of the tube used with D1's Robit bit RR77, in connection with the prior use relating to Terra-team Oy (D6 to D10). The bit and the tube were listed in the enclosed list D22a, and its verified translation D23. The newly filed product list of D22a and the picture of D21a were highly relevant and related to a company called "Helake", which had been purchased by Terra-Team Oy in 1994. This could be confirmed by Mr. Jari Rajalin who worked for Helake and then for Terra-Team and was named as a witness concerning the above mentioned facts. Although the new material was filed late, it was argued that according to the established case law the main issue relating to the admittance of documents into proceedings was their relevance. Thus, any relevant documents filed as a reaction to new submissions should be admitted.

(b) The Appellant argued that it was immediately apparent that D21a to D23 had nothing to do with the alleged prior uses to which D6 to D10 related. For example, the product numbers listed in D22a all related to components having the dimensions "72/49". D6, D9 and D10, on the other hand, all related exclusively to components having the dimensions "68/47", whilst D7 related to a component having the dimensions "78/57". In other words, any purported activities relating to product numbers 07144, etc., of D22a/D23 constituted a new allegation of prior use. Moreover, the Board was reminded that it was fully entitled to refrain from even examining the potential relevance of such a late-filed submission. Even if the Respondent's submissions were considered by the Board, there was no information as to when the prior use occurred, where, how or by whom. As such, the allegation of prior use had not been adequately substantiated and, accordingly, was inadmissible. Finally, given that the role of a witness was simply to corroborate previously submitted facts, and no such facts had been put forward, it was only proper that the Board should refuse to hear Mr. Rajalin.

VII.4 Admissibility of further Evidence

(a) The Respondent reiterated that a relevant document, when filed as a reaction to new submissions, had to be admitted to the proceedings. As to document D14, a conical rope thread coupling for a drill string was suggested. The coupling depicted in figure 2 was drawn very systematically and clearly showed an intended conicity of the thread. Since the crests were flattened, the crest radius could be interpreted as being infinite and the ratio between crest radius and thread pitch thus was well beyond 30%. The circular root portions provided a ratio of more than 30% as well. Moreover, the threaded coupling of document D15 was highly relevant, because it clearly taught the skilled person to enlarge the crest radius beyond 30% of the pitch of the thread if good fatigue resistance and wearability of the coupling were to be retained during percussive drilling: cf. pages 2 and 3 of D15. Document D17 concerned the standard dimensions to be used on rope threaded drill equipment for percussive rock drilling in 1991, and not only gave information as to the approximate millimetre values for product codes, but moreover gave a hint for the skilled person as to the ratio between the crest radius and the thread pitch according to claim 1 of the patent. Furthermore, the closest prior art D20 cited in the patent dealt with a drill bit for percussive drilling and contained all the pertinent information on percussive loads through hard formations. Tapered threads were described as being a "critical facet": cf. D20, column 2 and 3. With respect to the impact surfaces' positioning, claim 1 of the patent was "incomplete": cf. D22, expert opinion of Prof. Ulbrich.

(b) The Appellant argued that, according to the case law of the Boards of Appeal, late filed documents had to be prima facie relevant. The invention of the patent in suit pertained to percussive rock drilling, which required certain drill string elements, such as a particular thread profile and bit. However, D14 firstly did not relate to a conical thread, since the document remained completely silent as to why the profile of the draft in figure 2 might have had that form. Figures 5 and 6 of D14 were missing, but were shown, without thread conicity, on sheet 4/4 of the US-equivalent document D27. Thus, it was mere speculation that the draftsman intentionally drew conical threads in figure 2. Moreover, the crests in D14 were flattened. Thus, it was absurd to say that this was a "radius", taking into account the principle of a mind willing to understand claim 1 of the patent. Furthermore, D15, although pertaining to percussive rock drilling, was odd in that an asymmetric thread profile was suggested therein. During rock drilling, therefore, the coupling was kept together due to the forces transferred to the threads, which would lead to pitting and failure. However, D15 neither disclosed nor hinted at conical threads or impact surfaces. Document D17 related to a standard, and therefore would not be modified, since everyone in this particular filed would apply it. Thus, D17 would not have led to a conical thread. During rock drilling, the impact force and torque applied would cause the tightening of the thread coupling of D17. As already pointed out, the larger the diameter, the narrower the pitch angle, which made uncoupling more difficult. This is why the standard D17 is limited to a nominal thread diameter of 38 mm for a fixed pitch. Otherwise it could not be uncoupled. Therefore the Robit bit drawn in D1 could not be applied to D17. D20 was introduced by the examiner himself during the examination procedure, but this was not, however, agreed by the Appellant, since D20 was irrelevant. Contrary to the expert opinion D22, essential features were not missing in claim 1. However, if the Respondent's argument related to a clarity matter, it was no ground of opposition, and to the extent that it was a disguised Article 100(b) objection, no consent was given to the introduction of such new ground of opposition. Thus, the late filed documents D14, D15, D17, D20 and D22 should not be admitted into the proceedings.

VII.5 Inventive step

(a) The Respondent argued that a suitable starting point was document D17, which described the general standard of rope threads for percussive rock drilling. The subject-matter of claim 1 of the patent differed therefrom only in that a conical shape of a thread coupling was provided. Contrary to the Appellant's view, overburden drilling with pneumatic hammers was known in the art, and therefore the suitability of a thread coupling for percussive rock drilling as opposed to overburden drilling was overemphasized, because the tube-type drill strings were used for both drilling methods. However, D20 did not mention overburden drilling, but drilling "through hard formations": cf. D20, column 3, lines 28 to 29. Thus, the drill head assembly of D20 was both intended and suitable for rock percussive drilling. As was hinted at in column 2, lines 26 to 30 of D20, the tapered threads constituted an advantageous feature. Thus, taking D20 into consideration, it would have been obvious for the skilled person to modify D17 such that a conical thread was provided, and to arrive at the subject-matter of claim 1 of the patent. Moreover, the conical shape would also have been obvious from the Robit bit D1. Another starting point was either D20 or D1, both being suitable for percussive rock drilling. The thread coupling of claim 1 differed from their disclosure by having a different thread profile. The objective was to find an alternative thread. Hence, the characterising portion of claim 1 would have been obvious in the light of D17's or D15's advantageously taught ratio of thread crest to thread pitch. It was to be noted that the skilled person would not have any difficulties in choosing certain radius values from the ISO-standard D17, or in adapting the wall thickness of D20 (or D1) to the tubes described by D17 or D15. It was reiterated that claim 1 of the patent in suit did not define any wall thickness either. Therefore, claim 1 lacked an inventive step.

(b) Regarding the actual starting point of the invention according to the patent, the Appellant argued that, based on previously known rock percussive drill bits sensitive to breakage, uncoupled threads were required during percussive rock drilling in order to withstand the strains. As was immediately apparent from figure 2 of the patent, this had been achieved, in combination, by provision of both a conical and well rounded shape of the threads. The closest prior art was considered to be document D17, which related to percussive rock drilling. Document D20, however, dealt with earth drilling and not percussive rock drilling. The described "hard formations" could relate to clay, rubble or pebbles, but no rock drilling was disclosed; this was pure speculation. Only boulders might possibly be pushed aside by the rotary drill of D20. The drill head assembly of D20 was completely unsuitable for rock drilling, since its object was to provide a rigid unit: the conical tapering was to ensure that the all threads matched up along their surface. These contacts would cause failure in percussive rock drilling. Again reference was made to the technical meaning of overburden drilling as in D20, where very hard material at the bottom of the bore hole did not exist and, therefore, transmission of substantial forces between the drill string elements did not take place. During overburden drilling, only some percussive forces were transmitted by means of the impact surfaces but, in contrast to rock drilling, the drill string elements would be threaded together as tight as possible. This was entirely consistent with D20's teaching. Thus, starting from D17, there was firstly no motivation to turn to earth drilling, ie to overburden drilling of D20 (or D1). The conicity of D20 was combined with compressibility of particular tapered threads (cf. D20, column 2, lines 19 to 40 and column 7, lines 38 to 41), which could not give any advantage in a rope thread of D17. As to D1, there was no information about conicity, and hence no technical teaching which would have led in that direction. Finally, starting from the ISO-Standard D17 for a single rope thread, the maximum diameter was 38 mm, which was incompatible with the material dimensions of D20 (or the double rope thread bit of D1). It was true that claim 1 of the patent did not mention a particular diameter of the threads. However, claim 1 was clearly directed to percussive rock drilling and therefore had to be construed as being restricted thereto. Apart from that, no conicity was mentioned in D17, and since the skilled person would not deviate from compulsory standards, there was no teaching why the conicity of D20 (or D1) should be maintained. For the above reasons, D20, and the even further remote D1, could also not form the nearest prior art. Therefore, based on the prior art on file, claim 1 was not obvious and involved an inventive step.