Originally Posted by DaveSSS

Since bike chains are based on English units of measure, I prefer to use inch measurements. Campy's 132.6mm dimension converts to 5.220 inches. With the maximum allowed roller diameter of .306, .305 is a common size, but you may find some as small as .303. Take the .500 nominal pitch and subtract one roller diameter to get the nominal space between the rollers. That comes to .195 inch, if there was no clearance between the hole in the roller and the pin. My calipers find this dimension to be .205 inch, so that means that the holes are .010 inch larger than the pin. A new chain should measure about 5.205 inches between the rollers, which makes the 5.220 dimension only .3% longer. .5% would be 5.231 and .6% would be 5.236. My no-go gage made from a 6mm hex wrench measures an increase in the roller spacing of about .5%. By this time, the side clearance on the chain will be a lot greater than a new one. A new chain will usually have .004-.008 inch of clearance between the inner and outer plates. Twice the original clearance indicates a lot of wear.

Personally, I've never paid any attention to the Campy dimension after using Campy chains for 25 years. I did learn that these chains do not elongate very much, whether measured with a precision 12 inch rule or a full length measurement, so checking elongation is usually worthless. I have had others report significant elongation, but you never know how well maintained the chain is or what kind of conditions it was used in. I learned to measure the change in the roller spacing and the side clearance wear to decide when to change a chain, since the elongation measure was always under .25% on my chains.

I'm into a whole new ball game with SRAM AXS chains, but they aren't much different. They follow the #40 chain standard, with 5/16 (.3125) maximum sized rollers on the same .5 inch pitch. I've used them on cassettes and chain rings made for the #41 chains and haven't had a problem yet.