Calibration of A325 Bolts

Direct tension and torqued tension tests of 170 A325 bolts were carried out to determine the behavior and performance of individual A325 bolts. The major variables studied in the program included the effect of thread length between the thread run-out and the face of the nut, the effect of grip, continuous and incremental torquing, and reserve strength in tension after torquing. The behavior and performance of the bolts is examined, and typical data are presented. The results are related to the current Specification for Structural Joints Using ASTM A325 Bolts and have influenced the amount of nut rotation required when the turn-of-nut method of tightening is used. For usual grips, the grip length was found to have no appreciable effect on the load-elongation characteristics when the length of thread under the nut was approximately the same. Nut rotations greater than one-half turn from snug yielded little additional clasping force. Decreasing the amount of exposed thread under the nut results in a decrease in the deformation capacity of the bolt.