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 from 0 to 7. The Morse taper allows the bit to be mounted directly into the spindle of a drill, lathe tailstock, or (with the use of adapters) into the spindle of milling machines. It is a self-locking (or "self holding") taper of approximately 5/8" per foot that allows the torque to be transferred to the drill bit by the friction between the taper shank and the socket. The tang at the end of the taper is only for ejecting the drill bit from the spindle, with the aid of a drift. The arbor of a drill chuck is often a Morse taper and this allows the chuck assembly to be removed and directly replaced with the shank of a Morse taper drill bit. A range of sleeves may be used to bring the size of the smaller Morse tapers up to the size of the drive spindle's larger taper. Sockets are also available to extend the effective length of the drill as well as offering a variety of taper combinations. The detail image shows a Morse taper shank on a 16 mm diameter drill bit. Square taper drills were also used for large ratchet drills, for drilling large holes, or in thick plate. These bits would fit straight into a ratchet drill, and the ratchet drill would be used against a strong arm, for pressure to push the drill into the work piece. Some drills, wire wheels, etc. use a threaded shank. One example is cylindrical wire wheels meant to be pushed into a pipe of some sort to clean the inside of the pipe, but some ordinary, but mostly rather large, wood drills have threaded shanks as well. Small (about diameter) threaded drill bits and countersinks are common in aircraft metal work. Threaded drill bits may be held in drills meant to reach into very tight spaces, and threaded countersink cutters are widely used (along with finely adjustable depth stops) to create holes which put a matching rivet directly flush with the surface.