The collar is about 3mm in diameter by around 4-5mm in length, and it is fitted on a small piece of bent steel of the main chassis or a slide bar. This was on the underside of the deck. From what I can recall, we only found this by very closely looking at two mech's. The buffer compresses and allows one slide lever to move slightly to far.
It might be rectangular, rather than round!!!
As I mentioned, this was all a few years back.
