Union Butterfield 1500L(UNF) High-Speed Steel Hand Tap, Uncoated (Bright) Finish, Round Shank With Square End, Plug Chamfer, 1/4"-28 Thread Size Hand threading tap with straight flutes cuts threads in through holes and blind holes Left hand threads help prevent loosening in applications involving counterclockwise rotation Plug chamfer for easier starting and correct perpendicular alignment Available in UNC (Unified Coarse) or UNS (Unified Special) thread options for different applications High-speed steel is compatible with a variety of materials