You pull the knurled end, slip pointed end into the bbl, release the knurled end and then pull it out to read constriction. C=cylinder, M=modified, and F-Full. But it works for 12, 16, 20 gauge guns. Kiv figured it out and Euro Joe has everything.
Actually, Sandy...it hurts a lot more to pierce your ears. There aren't a lot of nerve endings in the nostrils. I danced a classical style of east indian dance called Orissi in performances, and have both sides of my nose pierced so that I could wear the silver nose chain and pin when I was younger. Nobody ever notices, because I don't wear nose pins when I'm not performing, and I haven't participated in this style for quite a few years now.