VAPKER 950 Pcs O Ring 0.5mm Watch Back Rubber Gasket set O-Ring Gasket Seal Replacement O-rings for Watch Backs 19 Different Sizes 12-30mm Rubber gasket set that is installed on the watch back case,can cover the gap between the watch band Play role in watch waterproof,suitable for watch repair and DIY watchmaker O-rings 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)