A torque wrench is a tool used to precisely set the force of a fastening such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms. A torque wrench is used where the tightness of screws and bolts is crucial. It allows the operator to measure the torque applied to the bolt so it can be matched to the specifications. This permits proper tension and loading of all parts. A torque wrench indirectly measures bolt tension. The technique suffers from inaccuracy due to inconsistent friction between the fastener and its mating hole. Measuring bolt tension (bolt stretch) is more accurate but most often torque is the only means of measurement possible.
A torque limiter is a mechanical overload protection device designed to protect mechanical equipment from damage. The torque limiter trips when an excessive torque load occurs and physically disconnects the drives and driven components almost instantaneously. This protects the machine from seeing excessive loading due to the accumulated rotational energy upstream of the torque limiter. The protection provided could mean avoiding expensive machine crashes or secondary disasters. This is a very applicable means of protection, but numerous factors need to be considered before the torque limiter method is chosen.