Danielson Crab, Clam and Shrimp Gauge Clam Gear - A simple plastic tool for measuring crab shells, clam shells, and shrimp carapace. Plastic gauge measures crab shells at 5-3/4, 6 and 6-1/4 in Diagrams gender Measures minimum clam shell size at 1-1/2 in Includes a 1-3/16 in shrimp carapace measure