ITEM NAME:750 Pieces 0.7mm Thick Dia Round O Ring Watch Case Back Gasket Size from 16mm to Description: 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: 0.7mm. 19 different sizes from 16 to 30 mm: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 15 = 750pcs) Specification: Material: Rubber Bag Size: Approx. 20 x 14cm/7.87 x 5.51inch Package Includes: 750 Pieces Washers O Rings Seals SKU: CKX0006539856039051.Rubber gasket set that is installed on the watch back case,can cover the gap between the watch band. 750 Pieces Washers O Rings Seals. Play role in watch waterproof,suitable for watch repair and DIY watchmaker.