I ordered a used set of parts off ebay and it came with a 520 (pretty sure) chain and rear sprocket. Do I have to get a front 520 thickness sprocket, or will the stock one work? My 525 chain is way too streched.

 

Yes, get the proper sprocket.

 

Cool, that's what I thought. Trying to decide if I wanted to get another 525 chain, or get a 520 front sprocket.

 

IF the used rear sprocket & chain are *as new*, go ahead & get the 520 front sprocket & have at it.

If you have ANY doubt whatsoever about the wear of the used sprocket &/or chain, buy new components.

For typical street riding replacement, I recommend the OEM 525 setup.