GearWrench 388709N 5/16 x 18 NC Taper Tap The GearWrench 388709N 5/16 x 18 NC Taper Tap features tapered cutting edges, which give a less aggressive cut than plug taps in small diameters. Manufactured from carbon steel, the GearWrench 388709N 5/16 x 18 NC Taper Tap has clear laser-etched size markings for easy identification.