For cleaning accumulated carbon and material build up inside the piston ring groove Suitable for use on pistons 51-127mm (2-5) Features three six-sided cutters suitable for both Metric and SAE pistons SAE - 1/16, 5/64, 1/8, 5/32, 3/16, 1/4 Metric - 2.0, 2.5, 3.0, 4.0, 4.5 (mm) Metric - 1.2, 1.5, 1.8, 2.8, 5.0, 5.5 (mm)