Bicycle Chain Pitch is a rather simple set of math. The pitch
relates to the distance between abutting rollers or rivets:
All bicycles made in recent times use a 1/2"
pitch, thus 1/2" between every set of consecutive rivets.
That has not always been true. Bicycles from the
World War I era actually used a 1" pitch and Shimano did
try and take a lead in the industry a few years back by introducing
a 10mm bicycle chain pitch at one time, but this innovation
did not catch on. Shimano was forced to return to the 1/2"
This is NOT to be confused with the width, when
having a discussion of bicycle chain sizes. Chain widths are
typically 1/8" or 3/32" and refer to the distance
between the two inner plates.
Increase in pitch due to wear is NOT a function
of the inner and outer plates stretch as some might like to suggest,
but rather wearing of the rivets that allows the outer plates
to separate further than originally designed.
Measuring a bicycle chain's pitch can be used to
identify chain wear and flag the need for a replacement chain
and/or cogs and chainrings.
See information on BICYCLE CHAIN LENGTH
Bicycle Chains: Length, Width, What's Best
to Buy etc.