GU10 has no thread to guide it into the holder, so the cap relies entirely on two pins entering two slots and then locking under a spring. That makes the geometry less forgiving than a screw cap: there is no self-alignment, and an error in any one of four dimensions produces a lamp that either will not enter or will not stay in.
Pin diameter sets whether the pin enters the slot at all. Pin spacing sets whether both pins enter simultaneously. Pin length sets how far the lamp seats and therefore how much contact pressure the springs see. Angular position, the rotation of the pin pair relative to the cap axis, sets whether the pins line up with the slots at the intended insertion angle. A gauge that checks only diameter catches perhaps a third of real failures.
The go member is a plate with holes at the maximum material pin condition; both pins must pass through it together. The no-go member has holes at the least material condition; neither pin may pass. Because the check is simultaneous, a bent cap that would pass either pin alone fails the pair, which is exactly the intent.
Dimensional gauging does not prove the twist lock works. A reference holder with the specified spring force is the only practical check, and it should be part of the routine for any new cap supplier because the failure mode, a lamp that drops out of a ceiling fitting, is a safety issue rather than a nuisance.
