This is a Kacchushi tsuba, an old iron tsuba with a slight watermarking technique. The tsuba features a round shape with a Tetsutsuchimeji (iron hammer mark) ground and Dotemimi (raised rim). The openwork pattern is interpreted as a side business of Kacchushi (armorers).

Kacchushi
Edo
Signed
Hozon (NBTHK)
Certifies a genuine fitting worth preserving: a correct signature, or, if unsigned, an identifiable era and school, with recognized artistic and craft value.
The NBTHK (Nihon Bijutsu Tōken Hozon Kyōkai, the Society for the Preservation of Japanese Art Swords) is a public-interest incorporated foundation founded in 1948 and supervised by Japan’s Agency for Cultural Affairs (Bunkachō); it is based at the Japanese Sword Museum in Tokyo. Its expert panels physically examine each submitted work (shinsa) and issue a certificate (kanteishō) ranking it by artistic and historical merit. NBTHK papers are the most widely recognized standard of authentication for Japanese swords and fittings.
NBTHK official siteReturns/exchanges/cancellations not accepted after shipment except for significant defects; if defective, return/exchange possible within 3 days of arrival (return shipping paid by customer).
This is a Kacchushi tsuba, an old iron tsuba with a slight watermarking technique. The tsuba features a round shape with a Tetsutsuchimeji (iron hammer mark) ground and Dotemimi (raised rim). The openwork pattern is interpreted as a side business of Kacchushi (armorers).

Kacchushi
Edo
Signed
Hozon (NBTHK)
Certifies a genuine fitting worth preserving: a correct signature, or, if unsigned, an identifiable era and school, with recognized artistic and craft value.
The NBTHK (Nihon Bijutsu Tōken Hozon Kyōkai, the Society for the Preservation of Japanese Art Swords) is a public-interest incorporated foundation founded in 1948 and supervised by Japan’s Agency for Cultural Affairs (Bunkachō); it is based at the Japanese Sword Museum in Tokyo. Its expert panels physically examine each submitted work (shinsa) and issue a certificate (kanteishō) ranking it by artistic and historical merit. NBTHK papers are the most widely recognized standard of authentication for Japanese swords and fittings.
NBTHK official siteReturns/exchanges/cancellations not accepted after shipment except for significant defects; if defective, return/exchange possible within 3 days of arrival (return shipping paid by customer).