The gauge bolt was also used as the condemnation level for other things, apart from being scrapped. DP for example! The gauge bolt will also tell the Armoutrers whether the body locking lugs are worn unevenly or whether one side of the rifle bolt has run through the hardened shoulder. The rifle will still function perfectly and is suitable for training but NOT for service use.
Anyway, there's a few examples of how the GAUGE, inspectors, breech bolts were used. Kept by the senior examiners, calibrated initially by the Chief Inspector of Small Arms at Woolwich (the CIA mark) and then annually or so at the calibration laboratory,
There, yet another few bits of useless Enfield information. Next question................