There is a drilling in the side of the plug in which you can put a size 3 Allen key or a Torx key T10 (usually found in the your BMW toolkit) in order to fit and remove it.
See tools
Also referred to as oil filler cap.
This crash protector for the cardan is made of cnc lathed...
These bar end weights made of stainless steel or aluminium...
The joint is the mount / adapter for the footrest...