3. Gage Pin Bolts of gage pins inserted into the fastener enables direct bolt extension measurement. The

A fully detailed description of an ultrasound system is given in Ref. 1. The technique is a property variant method and uses a transducer to send ultrasonic pulses through the fastener. The wave will echo off the far end and return. The time of the journey can be measured and is proportional to bolt length. As bolt length increases, the speed of sound decreases proportionally, further increasing journey time. The machine can process this information in terms of extension, stress, or tension. See Chapters 34 and 43 for further discussion.