These combination tools in TCT can be used in abrasive materials. They will drill countersink & finally counterbored a parallel hole. Designed to receive plug maker group 24. The drill diameter sizes are for a clearance hole only. For use with drilling machines or routers. T.C.T.1/4 in. Shank. Woodscrew Size. No. 10. Drill Diameter 7/32 in. Countersink Diameter. 12 mm. Drill Length. 20 mm.