US Patent 7302859 Device for showing tensile stress

In this device for indicating (10) pretensioning forces in a tensioning element (7), such as tie-down straps or tie-down ropes, the spring surrounds the tie bolt (3) which is located on the loop of the tie-down strap, and in response to weak forces describes a path (6) which is easily visible. The combination of two components which differ in shape allows the spring (1) to maintain its shape and spring constant. As a result, the pretensioning force is indicated directly, yet the spring is not subject to an additional load under high tensions but is protected by positive engagement.