All rubber construction with RS logo on the lid. Pictures and text provided by Loz Pavier.
This is one of the earliest rubber duraplugs available. As well as having the wrap over rubber lid, this base itself is also made out of soft rubber - unlike my other example which has a hard plastic base.
This version usually bends and contorts out of shape. The wrap over top is usually cut where the fitter forgets to put the cable through first. This was on a piece of education equipment so would have been wired by a familiar user in a technical department.
It is branded RS 'Radio Spares' - a still common supplier to the mainly electronics industry.
Inside the lid we read 'W.Haffenden, Sandwich, Kent' - the original trading company of Duraplug.