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had an issue with the 5th bolt hole presumably a thickness related issue. I had to put a very thin spacer between it and the crank
Shimming is part of the deal with Campag-style hidden fifth bolts, to take up the tolerance where the back of the crank is milled relative to the front of the spider tabs. All my UT cranks came with them, although they're not listed as a spare part or mentioned in the instructions. Obviously, most of my UT cranks got additional milling and in a prototyping set up it was easy enough to hold the tolerance required to eliminate the shims, because the part was jigged off the outside face of the spider tabs.
gbj_tester
Also interested to know about the Arc ring as my Fibrelyte (now dead) had an issue with the 5th bolt hole presumably a thickness related issue. I had to put a very thin spacer between it and the crank or else the bolt was not tight and the ring went wonky (technical term).