safety-stop

from The Century Dictionary.

• noun On an elevator or other hoisting-apparatus, an automatic device designed to prevent the machine from falling in case the rope or chain breaks.
• noun In firearms, a device to lock the hammer in order to prevent an accidental discharge.
• noun On a pulley or sheave, a stop to prevent running backward.
• noun In a spinning-machine, loom, etc., a device for arresting the motion in case of the breakage of a yarn, thread, or sliver.
• noun In a factory or mill, an apparatus by which the power can be shut off at the prime mover in case of accident in any department. In steam-plants the throttle may be closed by the fall of a weight, the weight being normally held up by a detent or catch which can be released by an electromagnet when a push-button or switch is thrown in any department. A brake may also be applied at the engine to shorten the time of the stop.
• noun A device to shut off power from the engine in case the governing mechanism should fail or break and the engine start to run at excessive speed.
• noun In sheet-metal work, an attachment to a press designed to arrest its motion by throwing the clutch, through which it receives power, out of gear in case the hand of the operator, in feeding the shells or blanks to the press, comes too near the dies for safety, or in case a shell chokes or jams the feed-motion or is wrongly presented to the dies.