Remember that this thread is focussed on the evolutions in iron tsuba, if I have understood it correctly.
Beautiful elaborate sukashi work in copper brass, gold, silver and gilt was evident in armor fittings from very early on. The artistic techniques were certainly there for soft metals.
Returning to iron, holes were drilled in the iron of kabuto plates and shapes were applied to the edges of iron haraidate-dai, upright holders for maedate. There were fashions for Kabuto bowls such as for the famous bulbous Akoda shape, indeed I sense fashions in Kiku chrysanthemum tsuba could have followed these as the triangular iron bowl plates curved outwards, following numbers such as 12, 16, 24, 32 or 62 etc. Kuruma ‘wheel’ tsuba (not Guruma, except inside compound words) also favoured set numbers of spokes, as did kiku chrysanthemum tsuba.
There may have been corresponding fashion changes in armor outfits that included kabuto and tsuba on swords. But in iron? Did they have the files for fine work?
Am I alone in seeing numbered spoke consistencies between kabuto plates and tsuba spokes?
Here is a tsuba for age consideration. What do we think? An evolution from older yamagane tsuba? The hitsu ana are contemporary with the tsuba.