Parlec C40-20TT4 Tapping Heads; Shank Type: Taper Shank; Shank Diameter (Inch): 2; Taper Size: CAT40; Minimum Tap Capacity (mm): M8; Minimum Tap Capacity (Inch): 5/16; Maximum Aluminum Tap Capacity (mm): M20; Maximum Aluminum Tap Capacity (Inch): 7/8