Top Plaza 750pcs O Ring Watch Back Gasket Rubber Seal Washers Size 16-30mm, 0.7mm This is a set of 750pcs new o-rings gaskets. For watch repair and must have a watch maker all sizes. 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)