Every so often the buffers on a locomotive need to be serviced where the stock is greased and the spring inspected for possble replacement.

In the picture above is a dismantled GWR buffer; note the curved cotter. There are two of these; the long one shewn and a shorter one that is out of shot.
There is a baseplate held on by four countersunk screws but these are only long enough to keep the buffer together so longer bolts are used to release the spring pressure gently.