Torque wrench

A torque wrench measures or limits the rotational force applied to a fastener. It helps tighten bolts and nuts to specified torque values.

Click torque wrench: An adjustable torque wrench that clicks when applied torque reaches its preset value. Its spring-loaded mechanism releases at the set torque, producing a distinct click.
Wheel lug nut: A threaded fastener that secures a vehicle wheel to its hub or wheel studs. Specified tightening helps secure wheels without overstressing studs or distorting components.
Torque: The rotational effect of a force about an axis, equal to force times perpendicular distance. A torque wrench controls this rotational quantity as it turns a fastener.
Impact wrench: A powered wrench that delivers rapid rotational impacts to turn fasteners. Its impacts make torque less directly controlled than with a measuring torque wrench.
Fastener preload uncertainty: Variation between the intended and actual clamping force in a tightened fastener. Friction means the same wrench torque can produce substantially different preload.
Beam torque wrench: A torque wrench that indicates torque through the deflection of a pointer against a calibrated scale. Its pointer shows applied torque continuously rather than signaling a preset threshold.
Cylinder head bolt: A fastener that clamps an engine cylinder head to its block. Even, prescribed tightening helps maintain the seal between the head and engine block.
Newton-metre: The SI unit of torque, equal to one newton of force acting at one metre from an axis. Torque specifications commonly express target values in newton-metres.
Torque screwdriver: A hand tool that limits or indicates torque while turning screws. It serves lower-torque screw joints that are poorly suited to most torque wrenches.
Thread friction: Resistance to motion between contacting screw threads during tightening or loosening. Thread friction consumes much of the applied torque and changes resulting preload.

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