It is a great thread, and these DAGGERS bring discussed are intriguing as they are vestigially recalling the form of much earlier PLUG BAYONETS with the distinctive hilt form, which as well explained by Fernando were designed to fit into the barrel of guns.
Most interesting is that in Spain, notably many examples from Albacete, continued being produced well into the 19th century, despite the fact that rifled gun barrels could no longer accept the hilts into them. The reason for this continued holding to the 'plug bayonet' form of the hilts, even though they were of course used as knives for hunting was the typical Spanish penchant for maintaining traditional styles. This was much the same as the continued use of the cup hilt rapier long after it was considered obsolete with the advent of the small sword.
The traditional presence of vestigial features in weaponry is well known in many cases, with one prime example being the pas d'ane in the small sword which served as a finger guard and securing loop in early small swords. By the end of the 18th century these became smaller but still present though no longer used, but retained as part of the traditional structure of these hilts.
If I may use another analogy beyond weaponry, in the US automotive design has been a key aspect culturally, particularly in the earlier years as design innovation was creative and artistic. Many autos of the 30s and later had features imitating aerodynamic designs and often copied notable elements from airplanes.
Some of the sportier cars had exhaust ports extending out of the hood area imitating those on some fighter planes. In the late 40s, early 1950s, the Buick automobile had a hood design with several 'ports' simply as decorative features, recalling those exhaust ports, but not of course, functional.
These 'vestigial' features, though not at all functional, clearly recalled the earlier auto designs, and by that virtue, the use of aircraft design and structural features in the auto design traditions in earlier years.
When I described a dagger, of plug bayonet 'form', it was noting that by appearance, it vestigially recalled the origins of the hilt design, and while NOT a plug bayonet in actuality, it remained associated in this sense.
I rest my case
On that note, Wayne, this is an OUTSTANDING example of this weapon type! especially witb the brass insert still in the aperture.