I did some checking on 3-arm chainrings as some folks questioned whether all the alloy ones are really compatible. The answer is Yes - sort of.
I have TA and Nervar arms and rings, Stronglight rings - no arms. I have neither the Campy 3-arm Grand Sport arms nor those rings.
The TA, Stronglight and Nervar outer rings all have the same size hole at the center, so the nut/sleeve from any brand chainring bolt will fit in any of them. However, the holes in the TA rings are countersunk, while the others are not, so the head of a TA bolt will protrude more when used on a Stronglight or Nervar ring than it does on a TA ring, but it will still secure the ring. There are two types of TA bolts, one that looks similar to Cyclotourist bolts, another that looks more like modern 5-arm bolts. Both will work with Stronglight or outer Nervar rings.
Nervar inner rings have a smaller hole than TA, Stronglight, or Nervar outer. This is because the Nervar 3-arm crank is designed for both chainrings to mount inside the arms, like with old cottered steel cranks. The sleeve on Nervar bolts actually fits into the outside of the crankarm. The bolt part, which has a smaller diameter, is inserted into the inside of the inner ring. It looks like one could use a Nervar inner on TA arms, but one would have to use a Nervar bolt or the newer looking TA bolt, and the latter would have to be installed "backward", i.e. with the sleeve on the outside.
Does anyone have any firsthand information about the compatibility of Campy 3-hole rings with TA, Stronglight or Nervar arms?
Regards,
Jerry Moos
Big Spring, TX