@Exige is the closest. It's common, found somewhere where moisture will add to the aging process... And its zoomed im, its about 3-4cm across.
Looks like one of these but too much taper and too large at 3-4 cms... https://www.wickes.co.uk/Wickes-End-Feed-Stop-End-Cap---22mm-Pack-of-10/p/137804