Brush material and size: Steel, brass, nylon - 6.35, 9.5, 12.7, 15.9, 19 and 25.4 mm. Each brush has a 1/4" hex drive shank. A Quick release screwdriver with a comfortable handle. Also includes a 6" extension with a quick release chuck. Suitable for numerous uses including removing carbon cleaning from internal threads or pipes and cleaning drilled holes.