Drill bit shank The name comes from the German "Stecken – Drehen – Sichern" (Insert – Twist – Secure). In German-speaking countries the back-formation "Spannen durch System" (Clamping System) is used, though Bosch uses "Special Direct System" for international purposes. The triangle shank is almost always made by machining three flats on round bar stock. It is intended as a minor modification of a straight shank, still allowing it to be held in a 3-jaw drill chuck, but allowing higher torque transmission and limited slipping. The Morse taper twist drill bits pictured right are used in metalworking. The full range of tapers is
Drill bit sizes for jobber-length straight-shank twist drill bits from 1/64 inch through 1 inch in 1/64 inch increments. For Morse taper-shank drill bits, the standard continues in 1/64 inch increments up to 1¾ inch, then 1/32 inch increments up to 2¼ inch, 1/16 inch increments up to 3 inches, 1/8 inch increments up to 3¼ inches, and a single 1/4 inch increment to 3½ inches. One aspect of this method of sizing is that the size increment between drill bits becomes larger as bit sizes get smaller: 100% for the step from 1/64th to 1/32nd, but a much smaller percentage between 1