The rubber sucker that sits on one prong of the internal mirror to secure it against the windscreen to stop vibration and movement. Fitted from 1965 until design change in 1996. A black sucker
24A1535 was fitted on a twin ball stem from Oct 1964 when cars had single end hinged sunvisors until late 1965.
Late 1965 when the sunvisors with a hinge at both ends were introduced the mirrors with a revised 3 ball stem with a clear sucker
CRT10004 started appearing.