Hi Jim,
"Figure 1.A
Naval Officers' Sword ca. 1795 (Francis Thurkle)
One of the more commonly encountered Thurkle hiltings featuring a counter guard containing a pierced diamond- see detail."
Thats about it, Glen is correct he doesn't state that it is exclusive to Thurkle, just that it is common to them. Good eye on the square and compass motif. Actually look at the reflection off the ferrule, looks even closer

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Hi Glen,
Please go ahead and link, I can only think of one forum where this isn't allowed.
All the Best
Jeff