1-1/2 Inch Cutting Depthelectron Beam Welded M-2 High Speed Steelspring Steel Back, Positive Rake Toothcutting Edge Rc 63-65, Vari-Tooth Design suggested Rpm:115 For Mild Steel, 55 For Tool And Stainless Steel, 75 For Cast Iron, 150 For Brass And 170 For Aluminum.