About this detail of the Tiger
The Tiger's mantlet was supported by trunnions embedded in the turret walls. This cutaway diagram, extracted from the Turret Manual, shows the left side of the mantlet. It has a bearing hole where a trunnion can be inserted.
As you can see, the rear side of the bearing can be removed; this was done only to separate the mantlet from the turret.
Within the bearing there is a spherical steel bushing, labelled 'Buchse'.
This is a model of the Tiger's bushings. Each consisted of an inner sleeve and an outer spherical housing. The Pz4 had a similar arrangement, and its inner sleeves were made of brass, so I assume the same material was used here.
This model of a turret, with the mantlet removed, shows a bushing placed upon its trunnion. The small item to the right is a filling tap for lubrication grease for the bushing. They were originally painted red, as shown in the model.
These filling taps are numbered (45) on the Tiger Lubrication Chart. They should be filled with grease "every two to three months".