30 Plastic Watch Crystals. This is a new set of 30 plastic watch crystals. These are high gloss and weather resistant. Each measures approximately 31.2 mm in diameter. We work hard to update our descriptions and pictures of our merchandise. As part of a process of ongoing innovation by our suppliers, newer versions of the item shown may be shipped before we are able to complete an update. As a result there may be a slight variation in color and design.