The leaves of the 66MA feeler gauge set are tempered steel, 12.7mm(1/2in) wide and 77mm(3in) long. Each one is clearly marked and easily removed and replaced. There is a locking device on the case. The 66MA features 20 leaves from 0.05mm to 1mm in 0.05mm steps. Feeler gauges are used to adjust tappets, spark plugs, distributor points, checking bearing clearances and gear play, fitting pistons, rings and pins and gauging narrow slots.