Handy to carry around due to its size and weight Made from durable plastic Measures in diamond carat and pearl grain Perfect in finding the rough size of stones or pearls This gauge is really handy to carry around with you as its only the size of a card. Made from hard durable plastic, it is used to find the rough size of stones or pearls even if they are in a setting. The appropriate sized hole is placed over the stone and an indication of the stone size/weight is obtained. These gauges may also be used to suggest what size stone a setting will accommodate. The gauge is placed over the setting and each hole is placed across the top until the nearest size is reached. Carat measurements from .016 to 6.15 and grain .518 to 41.06. 1 grain = 64.