The hub cap protects the bearing from the ingress of dust and at the same time acts as a shroud for the mounting components.
The wheel hub is fitted with an inside groove to retain the hub cap on its segmented edge.
The hub cap is pushed into position by hand and it can be removed by levering it away at the relieved point with a screw driver.
The needle bearings are greased on assembly which should be ample for permanent lubrication.