I use a 14 or 16, whatever is available, and change them when I start having problems with the thread shredding or I hear a sort of "popping" sound, which tells me the needle is getting dull. I've done 6 or 7 quilts with one needle! Needles are just something I don't deal with unless needed - I can't see wasting a perfectly good needle if it works LOL! Same with my DSM, as far as changing the needle.