Originally Posted by
753proguy
The single groove means British threads, though. No groove MIGHT be Italian, or French, or even British if the hub is old enough.
Initially, Campagnolo put no markings on the rear (Record) hubs for threading type. Then they went to the single groove for BSC (no groove could still be Italian or French during that time period), then they eventually went with the very complete call-outs around the freewheel mounting surface for the three types. But I'm not sure whether Tipo hubs did exactly the same thing (I guess I would guess that they did, however).
Both French and Italian lacked the groove. But an Italian freewheel wouldn't even engage the threads on a French thread hub, and a French thread freewheel couldn't even begin to thread onto an Italian hub, so it wasn't really an issue.