Abstract: An intelligent bolt includes a head region and a threaded region. The head region includes a bolt cavity. A distance between the head region and a bottom end of the cavity changes in operation as a function of longitudinal stress applied between the threaded region and the head region, and the bolt includes a sensor arrangement for measuring changes in the distance. A distal end of the sensor arrangement is disposed adjacent to the bottom end, wherein changes in spatial position of the bottom end relative to the distal end occur as a function of changes in the stress applied to the bolt to define a gap “G” whose size varies depending upon the stress. Interrogating radiation transmission in operation via the gap “G” from a source to a corresponding radiation sensor of the arrangement generates a stress measurement signal that is processed for wireless communication.