This gauge provides two useful, legal measurements. Carapace measurement of 3" for lobster and a stone crab claw measurement of 2-3/4" can be made in a matter of seconds, quickly and accurately! NO OTHER GAUGE DOES THIS. The gauge is made of the highest quality impact resistant plastic available and is a caliper type gauge for legal accuracy. The hole on the end is perfect for use with a lanyard - thus allowing fishermen or divers to attach it to their wrists or belts for convenient use. Lobster gauge are for southern lobsters.