1 BIG piece of advice from a long time serger user - DO NOT repeat DO NOT sew over pins unless you want to replace your upper knife often & risk a repair bill. I know a lot of people will say "I sew over pins all the time & nothing has happened" YET !! As the saying goes "you can pay me now or you can pay me later" On certain things yes, you would want to disengage the knife & there should a pin that you pull out & your knife should turn so that it is not in use.