The eccentric strap had a round glass oil-cup with a brass base that screwed into the strap.

On the eccentric straps, of which there were two on each side of the engine, the figures FB and FT (Fore bottom and fore top) and correspondingly AB and AT appeared.

In order to do so an eccentric usually has a groove at its circumference around which is closely fitted a circular collar (eccentric strap) attached to which an eccentric rod is suspended in such a way that its other end can impart the required reciprocating motion.