Abstract: A tool for the application of selected torque to the polygonal head of a bolt, to a nut or to an analogous component has a first portion which is a snug fit on the polygonal part of the component, and a polygonal second portion which can be engaged and rotated by a wrench. The material of the tool is more readily deformable than the material of the component and the material of the wrench so that the wrench deforms the second portion and/or the component deforms the first portion of the tool when the component offers a selected resistance to further rotation, i.e., in response to the application of a selected torque to the component. The first portion can be bonded or molded to the torque-receiving part of the component to be rotated, and the second portion can be coated with a film of a color different from that of the second portion to facilitate visual determination of the condition of the second portion.