As you would expect, it has two parts, with two screw fixing to each part. Both parts are entirely plastic. The part which fits on the frame forms a pin or peg with an enlarged bulbous end and this pin pushes into the part mounted on the door.
The part on the door, is circular apart from the mounting lugs, with a hole in its centre, surounded by fingers (rather like an inward pointing star). The pin pushes into the centre, and is then held by the bulbous end of the fingers and the inverted star fingers.
Anyone know what the item I am looking for is called please?