An 80mm watch glass typically refers to a circular, slightly concave piece of glassware used as a versatile laboratory staple or beaker cover. If you are instead looking for a wrist watch crystal, 0.80mm is a common thickness for replacement sapphire or mineral glass.Laboratory Watch Glasses (80mm Diameter)These are primarily used in chemistry labs to evaporate liquids, weigh solids, or cover beakers to prevent dust contamination.