Don't know. Is there data printed on your bar? Should tell you the chain size you need. What size chain & bar & sprocket your saw come with?
Look at your bar it will tell you what chain you need. I bet your running .325 chain .058. No you can't just switch sprockets as your bar is still not the same as new chain. And Yea 72dl in 3/8 is 20" if your .325 72dl is 18" I agree with shawn.
These are very handy to have in the shop when you have random chains and bars and you want to know chain pitch and gauge and bar gauge. Cheers!
Well bars are usually engraved or stamped Chains are a bit harder to identify if you dont know your chains.
Well gauge chain is hard. I only have .050 for anything and thats most common here. In 3/8 or .325 or lopro 3/8