Feeler gauges are used to adjust tappets, spark plugs, distributor points, check bearing clearances and gear play, fitting pistons, rings and pins and gauging narrow slots. Leaves are tempered steel, easily removed and replaced. There is a locking device on all sets.Millimetre Reading Gauges with Straight leaves 12.7 x 77mmNo. of leaves: 13 Range: 0.03 - 0.5mm ( 0.03- 0.10 by 0.01 mm steps, 0.15, 0.20 to 0.50 by 0.1 mm steps)