Yosoo 950pcs O Ring Watch Back Gasket Rubber Seal Washers Set Watch Gaskets kit Replacement O-Rings for Watch Backs Size 12-30mm, 0.5mm Rubber gasket set that is installed on the watch back case,can cover the gap between the watch band and movement Play role in watch waterproof,suitable for watch repair and DIY watchmaker This is a set of 950pcs new o-rings gaskets,the o-rings different 19 sizes thickness 0.5mm 19 different sizes from 12 to 30 mm: 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30mm. Comes 50pcs each size in a poly bag (total: 50pcs x 19 = 950pcs)