Roller Chain Identification
Identifying By Markings - Easiest Option
Most roller chain has the size stamped right into the side plates. You may see something like "40", "C2080H" or "10B" stamped in, which the industry number that represents the chain size. Old chains will most likely need to be cleaned in order to see the size. Not every side plate has the marking, therefore you'll need you cleanup several side plates.
Identify By Measuring Old Chain
If there are no markings, then measuring your old chain is the next option. You'll need a set of calipers (No ruler - no tape measure) to accurately get the required dimensions. Many chains have close dimensions, so its imperative that you use calipers. At first the most important dimensions that are needed is the Pitch, Roller Diameter & Inner Width as shown in the diagram below. After these dimensions are obtained, then you can compare against the roller chain size chart. Download a pdf chain template to fill in all measurements.