Rock bolting provides a supplement or alternative to conventional timber and steel supports. The tensile strength of the bolts lies within a range established by manufacturing quality control. Rock bolt testing determines the ability of the rock, anchor and individual bolt as an assembly to accept load. The.test is performed to the yield strength of the bolt or anchor and deflection is observed. The anchorage index, inches deflection per 1000 lb load increment, is a measure of anchorage quality. This allows comparison with anchorages under ideal conditions. It also permits comparative assessment of roof bolt anchors in a particular environment.