The term Chain gauge is used to describe the width of the drive links on your chainsaw and comes in sizes like .050”, .063” etc. and must match the groove in your bar. The length of your chain is determined by counting the drive links,one example would be 70 links = 72”.
Make sure you check your owners manual when ordering new chain, so you get the right chain size for your power saw. If you don't have a way of cutting the chain and splicing it back together be sure to check the number of drive links you need. You can find this by looking at your bar to see the bar length. Some chainsaw bars have the length stamped on them, but make sure to check your owners manual to see how to calculate the actual chain length based on the bar plus the base to get the right length of chain needed.
Sprocket mounted in bar tip and showing groove for drive links to ride in.