The R63 bulbs Rubin (Rossmann) bulbs fit mechanically almost not in the sockets. The contacts in the socket are so short that you have to purely turn the pears with a lot of power. In the first test, there was simply no contact and the lights remained dark. At the same time the lamp is front so narrow that you can touch the bulb only at the front screw while. One has the feeling to have when reindrehen expend so much energy that the glass of the bulb shatters almost - very uncomfortable.
Once you have overcome the problem is everything ok. The clamping mechanism acts robust and does what it should.