Just going through "Armi Bianche Italiene" (Boccia & Coelho, 1975) and there are a number of 'crab claw' type daggers of this type, some listed as 'pugnale da duello'. Most (#575/7677/78) are from N Italy and seem to range 1570-1600.
Most interesting that one has virtually the same parallel ridges inside the ring and a peak at the top of the ridge. Another has three ridges inside; another ridges on the outside. In another the ridges have a more stylized effect.
I would be inclined to submit these are more decorative nuances and perhaps elements of 'personalized' style of certain makers? or if these are indeed 'duelling' daggers, perhaps some now forgotten 'signal' known to this particular social strata of the times. Intriguing , yes?
