240 New Men's Mineral Watch Crystals. This is a new set of 240 men's flat mineral watch crystals in 20 different sizes. Each flat natural mineral watch crystal measures 1 mm thick. You receive twelve of each size: 26, 26.25, 26.5, 26.75, 27, 27.25, 27.5, 27.75, 28, 28.25, 28.5, 28.75, 29, 29.25, 29.5, 29.75, 30, 30.25, 30.5 and 30.75 mm.