The bearing is a simple o-ring. No ball bearing inside. The plus side is that it's more simple and more likely inert, the bad side is that the friction is high (and probably the o-ring gets worn down way more than it would have to with a ball bearing system). When I read "bearing" I really expected a ball bearing into the stopper with a PTFE core and joint separating the axis from the ball bearing.
thank you for your job!