N Cook wrote:
No photo available.
Retaining rings are thick black plastic like the back rings of LED clips but
scaled up to go over the brass barrel of the socket , rather than normal
threaded bush, and this ring then sits under a lip around this barrel
after being forced over the lip so firmly in place. Although with fair
amount of finger force you can rotate the whole socket in the hole in the
thin steel chassis plate .



Are you sure it`s not a bayonet fitting? There is a pretty common jack
socket used on many mixing desks so designed.

Ron(UK)

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