Hello Richard, your headset matches the one on page 228 of the repro Emilio
Bozzi catalogue from Chuck Schmidt. It is, I believe, A ''W.A. Corsa
Decagonale'' Tipo Thompson. The only difference I can see it that your top
nut has serrations in the recess. A minor difference perhaps not picked up
by the industrial artist who did the original drawing. Hope this helps.
Mark Stevens, Evanton, Scotland