GearWrench 82855N 18mm x 2.50 NC Plug Tap The GearWrench 82855N 18mm x 2.50 NC Plug Tap features tapered cutting edges, which give a less aggressive cut than plug taps in small diameters. Manufactured from carbon steel, the GearWrench 82855N 18mm x 2.50 NC Plug Tap has clear laser-etched size markings for easy identification.