A torque angle gauge measures rotation in degrees during bolt tightening. Many modern cars use torque-to-yield (TTY) bolts for cylinder heads and main bearings. These bolts must be tightened to a specific torque value first, followed by a precise amount of rotation, like 90 or 180 degrees. The gauge fits between your socket wrench and the socket, showing you the exact angle as you turn the handle.
The gauge features a round dial face, an adjustable indicator needle, and a magnetic or clamp-on stop arm. The stop arm locks against a nearby engine part to prevent the dial face from spinning with the wrench. Once locked, you zero the dial and sweep the wrench until you hit the target angle. Trying to guess a 90-degree turn by eye is risky and can lead to uneven head clamping, blown head gaskets, or snapped bolts.