Three things for me that point to the tsuba being made by Sadahiro are as follows. 1: Ko Sukashi, which is very common in the works of Sadahiro. 2: Heavy tekkotsu that is carved or chiselled from the iron, as opposed to dense iron or impurities left in under the surface of the tsuba in the forging process. This is an unusual characteristic and one common to the Nidai Sadahiro. 3: Fold layers visible in the mimi and the ko sukashi. It is said that the ita plate of Sadahiro is folded so many times, that the mimi can look like a cotton spool with the multitude of layers on the side.
Add to that the dense black iron and the Nademaru gata shape, both common traits of Sadahiro and I believe that this attribution is correct. A general description of the guard is as follows.
Owari tsuba by Sadahiro – Tetsu Tsuchimei Ji, Nademarugata (papered as Shitogi gata or Millet shape), The mimi is kakumimi and finished in dote-mimi, tekkotsu is clear in both the mimi and the hira and is chiselled from the tsuba. Also there is the clear layered lines seen in the mimi. Lead ategane, Ryohitsu Shitate ( finished with two Hitsu ana ). Shu-mei attribution ( red lacquer signature 銘朱漆 ) to Sadahiro. There is also a Kao (花押) though I have no idea what this reads. This tsuba is similar in design to the work of the second Yamakichibei. The first Sadahiro was one of the great Owari tsubako and worked in the early or mid Edo period. The theme may be a radial design of spokes and or a form of wheel design but it is obscure to say the least and open to interpretation.
The dimensions are 89mm x 80mm x 3mm ( dote-mimi is 4.5mm )
One last point of interest is the box the tsuba lives in. Is has a seal and attribution and having the seal translated with help from friends Japan I got the following.
The seal on the front of the box is believed to read Kin Ji Kyo Kura 欽持恭蔵, and the meaning of the seal may be “to possess respectfully, to store reverently”. This may represent a previous owner’s attitude toward the tsuba or his personal motto”.
This is an interesting and bold tsuba.and one of which I am very fond.