This gauge is the quick and accurate way to measure your catch. Notched to measure crab shells a 5-3/4", 6" and 6-1/4", it also diagrams the gender for easy identification. A 1-1/2" ring makes it easy to verify the most commonly required minimum clam shell size. It also features a 1-3/16" shrimp carapace measure and a hole for attaching a lanyard.