Genuine correct NOS 4mm speaker sockets, for Rogers, Harbeth, LS3/5A, QUAD & many others.
These are insulated post type, with 2 insulators, one inside and another outside.
Accepts 4mm plugs. Threaded part approx 3.5mm, wire hole approx 2mm.
DO NOT CONFUSE THESE WITH MANY CHEAP VERY INFERIOR CHINESE COPIES, LIKE CLIFF etc.