Lampholder requirements in IEC 60061 part 2 include mechanical tests that have nothing to do with whether the lamp fits. The torque test checks that the holder body, the contact assembly and the mounting do not rotate or crack when a lamp is tightened, and when the holder itself is installed in a fixture.
The first is applied through a gauge cap inserted in the holder, simulating a lamp being screwed home. It tests the grip of the holder on the cap and the strength of the contact carrier. The second is applied to the holder body as it would be during installation in a luminaire. The magnitudes depend on cap size: a small cap sees a small torque, a large one sees more, because the lever arm and the expected hand force both scale.
Rotation of the contact carrier is the most common failure and the most dangerous, because the contacts can end up closer together than designed. Cracking of the body around the mounting screws is the second, and it typically appears only after thermal cycling. A holder that passes torque cold and fails after a temperature cycle has a material problem, not a design problem.
Apply the torque slowly, hold it for the specified time, and inspect for movement with a witness mark. A torque wrench that is applied in a single jerk measures the peak, not the sustained load, and will pass holders that creep under a steady hand.
