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 same concept that names like "general-purpose" and "multipurpose" reflect. Extended-reach or long-series drills are commonly called aircraft-length from their original use in manufacturing riveted aluminum aircraft. For bits thicker than a minimum size such as 1/8 inch, they are available in fixed lengths such as 6, 8, 12, or 18 inches rather than the progressive lengths of jobber drills. The image shows a long-series drill compared to its diametric equivalents, all are in diameter. The equivalent Morse taper drill shown in the middle is of the usual length for a taper-shank drill. The lower drill bit is the "jobber" or