GearWrench 388731N 12mm x 1.50 NF Plug Tap The GearWrench 388731N 12mm x 1.50 NF Plug Tap features tapered cutting edges, which give a less aggressive cut than plug taps in small diameters. Manufactured from carbon steel, the GearWrench 388731N 12mm x 1.50 NF Plug Tap has clear laser-etched size markings for easy identification.