Ratcheting Screwdrivers
Some manual screwdrivers have a ratchet action whereby the screwdriver blade is locked to the handle for clockwise rotation, but uncoupled for counterclockwise rotation when set for tightening screws; and vice versa for loosening.
Manual screw drivers, often colloquially called "Yankee Screwdrivers", with a "spiral ratchet" mechanism to transform linear motion into rotational motion also exist, and predate electric screwdrivers. The user pushes the handle toward the workpiece, causing a pawl in a spiral groove to rotate the shank and the removable bit. The ratchet can be set to rotate left or right with each push, or can be locked so that the tool can be used like a conventional screwdriver. Once very popular, these spiral ratchet drivers, using proprietary bits, have been largely discontinued by manufacturers such as Stanley, although one can still find them at vintage tool auctions. Some companies now offer a modernized version that uses standard 1/4-inch hex shank power tool bits. Since a variety of drill bits are available in this format, it allows the tool to do double duty as a "push drill" or Persian drill. One disadvantage is that if dislocated by slipping out of the screw, the resultant sudden extension of the spring may cause the bit to scratch or otherwise damage the workpiece.
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