These machine bits encompass two wings, a centre point and two scribers. Tungsten carbide tipped (TCT) for extensive drilling of plastics of soft to medium density and particle boards. The scribe provides a very clean entrance hole. Not to be used on hard dense materials like laminate covered board, Wareite, phenolic Tufnol and GRP (fibreglass). For these materials, choose from Group 421 tools which don?t have scribers. Only for use in drilling machines.