Fig. 1040.
Fig. 1041.
In the smaller sizes of twist drill, the stem or shank is made parallel, as in [Fig. 1040], while in the larger sizes it is made taper, as in [Fig. 1041], for reasons which will appear hereafter.
The taper shanks of twist drills are given a standard degree of taper of 5⁄8 inch per foot of length, which is termed the Morse taper. A former standard, termed the American standard, is still used to a limited extent, its degree of taper being 9⁄16 inch per foot.
Fig. 1042.