This easy to read gauge is made from tough ABS plastic & allows the user to quickly measure the size of nuts, bolts, & screws. Can also be used to determine whether a nut is UNC or UNF, taking the trial & error away from selecting the correct replacement size. Measurements include: internal diameter of UNC & UNF nuts; diameter of metric & imperial bolts; length of rounded, pan, countersunk, set screws, together with hex head bolts; reference chart for hex cap screws