It is often necessary to punch small keyways, or other slots of similar shape, into small pins and bolts, to avoid drilling; and, after punching, thin drifts of various lengths and thicknesses are driven into the slots to enlarge them to the required dimensions. A thin drift, having curved extremities to resist the hammering, is shown by Fig. 210.

Drifts are made also of circular, oval, rectangular, hexagonal, and octagonal transverse sections; and are used for drifting nuts, joint-pin holes, small connecting-rod eyes, lever-bosses, fork-joints, spanners, machine-handles, and several other articles, when the object is to economise the time that would be occupied in shaping with more expensive machinery.

Whatever may be the particular shape of the drift, it should be of excellent steel, very smooth, and as near to straightness as can be made. For general work, it may be stated that the angle subtended by any two opposite sides of a finishing drift should not exceed one or two degrees, which is termed very slightly taper.

Drifts for enlarging the holes in large work during forging should be very taper, the angle subtended by the sides being about fifteen degrees.