Centre gouges consist of small chisels having curved cutting edges, and are of different sizes, according to their intended uses. Gouges of this character, to be held in one hand, are represented by Fig. 275 ; a tool of this sort is used for cutting away the metal at the mouth of a recess that has been drilled with a small drill and requires coning; after sufficient metal is cut away by the gouge, a coning punch is hammered into the recess until the desired form is obtained. Gouge chisels are used also for centring and channelling; when employed for centring, a gouge is the tool for enlarging a conical recess at only one side, by which means the centre or middle of the recess is put into another place; gouges for channelling are made from a sixteenth to a quarter of an inch wide at the cutting part, and are required to cut or form grooves into the sides of centre recesses to admit oil for lubrication.