A torque specification chart explains the correct torque for a variety of nut and bolt types. The charts tell mechanics, builders and assembly workers how to tighten each nut and bolt for maximum efficacy. Most charts identify bolts or nuts by size and the number of threads per inch. Depending on the chart, the torque specifications may include clamp load, proof load and the correct tightening torque.
The assembly torque is one of the most important numbers on the spec chart. It indicates the maximum amount of torque that a nut or bolt can take before its performance is negatively affected. Some charts provide the acceptable torque range for each bolt. Torque specification charts occasionally include the proof load, which refers to the load that the bolt has been proven to handle. The bolt should not stretch, deform or break under the proof load. Torque values are always given in foot-pounds.
The information on a torque specification chart varies by manufacturer and the intended application. Some charts provide the dry torque value for plain bolts; others provide specific numbers for waxed bolts and galvanized bolts. Most charts offer individual values for different grades and materials of the same bolt or nut size.