Tool-Flo 1270997 Helical Flute Thread Mills; Material: Carbide ; Thread Size (Inch): 1/4-18 - 3/8-18 ; Thread Type: Internal; External ; Shank Diameter (Decimal Inch): 0.3120 ; Cutting Diameter (Decimal Inch): 0.3120 ; Length Of Cut (Decimal Inch - 4