Which of the following is determined by measuring bolt length change while torquing a bolt?

The correct choice is related to the concept of torque stretch, which refers to the elongation of a bolt when it is tightened to a specific torque. When a bolt is torqued, it undergoes tension, and the amount of stretch can be measured to ensure that the bolt is properly tightened without exceeding its yield point.

Measuring the length change of the bolt during this process gives valuable insight into how much the bolt has stretched under tension. This principle is crucial because it ensures that the fastener is tightened adequately to hold components together while preventing any damage caused by over-torquing.

Other concepts, such as torque-to-yield, involve a related but distinct methodology where bolts are stretched beyond their elastic limit to improve clamping force, but this is not directly measured in the same way during initial tightening. The torquing sequence refers to the order in which bolts are tightened, which helps prevent warping or distortion, and torque specification indicates the torque values for fasteners, providing guidelines for acceptable ranges, rather than measuring the actual elongation of a bolt. Understanding torque stretch helps mechanics ensure that fasteners achieve the correct clamping force, which is critical in maintaining the integrity and safety of bus components.