These Horotec watch case tool pins come in 7 different styles (styles sold separately) to fit a variety of different notched, screw-on watch case backs. The pins friction in and out of the tools and have a base diameter of 5.0mm. The available pins are round, flat, square, grooved, long-round and long-square. They will fit many Horotec case back tools including but not limited to item numbers 64.0713 and 64.0920 (MSA 07.013 & MSA 07.320). Sold per piece.