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a hand tool that is widely used in fitting and assembling operations to screw and unscrew bolts, nuts, and other threaded connections. A wrench has a jaw or contoured projections and recesses that grip the objects. The principal varieties are simple wrenches with single and double ends, lever types, socket wrenches, and adjustable (monkey) wrenches.
Torque wrenches (both self-releasing and indicator types), which are used when assembling vital screw connections on instruments, motors, lathes, and so on, are the most advanced and satisfactory types of wrench. Indicating wrenches have a torque indicator that gives a light or sound signal when the desired torque value is reached. Self-releasing wrenches automatically disengage when the specified torque is reached, thus avoiding stripping the threads. Nut wrenches are extensively used in automated assembly.