For checking seat rail wear limits as per FAA Airworthiness Directive 2011-10-09, Effective 06/17/2011 Seat Rail Directive and its predecessor A.D. The gauge is used for inspection of seat rail wear in Cessna aircraft. It’s designed to measure the actual radius wear near the seat stop holes. Notice the different sized step the corner. The size applies to the .42 diameter limits referred to by the A.D. The .020 upper surface wear allowance allowed by the A.D. is designed into the gauge. 1 lbs (0.5Kg) shipping weight.