Hi
No problem!
I have only seen these (ribbed) buttons on things like the RAF Yacht Club, which I think are the same but with 'YC' on them. Although very early 1920s there were bronzed and leather buttons still in use, I've not really found black plastic until mid-WW2, when they were made specifically for the Tropical Service Dress, but these were Kings Crown with a smooth base. I've had similar use attached to the ribbed version and 1920s but nothing to confirm it.
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