A copper alloy (sentoku) example in The Metropolitan Museum of Art posits the motif as “108 human sins in the guise of monkeys” (46.122.77). Signed Hishū Yagami-Jū Mitsuhiro, it and other examples include a silver alloy (shibuichi) tsuba in The Walters Art Museum (from Noda, rather than Yagami, in Hizen province) signed the same (51.133), a second (unsigned and in the nanban manner with patterned seppa-dai) in the Walters has a mimi surrounding the open worked plate, an iron nanban tsuba in the Seattle Art Museum (37.44), a photographed iron nanban tsuba in the J. Paul Getty Museum (56538), and an iron tsuba in the Museum of Fine Arts Boston signed Yagami Shoyoken Mitsuhiro (13.1769).
Of the above examples in prominent public collections, the sentoku [copper alloy] and shibuichi [silver alloy] examples appear to be later generations of the same Mitsuhiro line. The present example (unsigned) and the Boston example (signed Yagami Shoyoken Mitsuhiro) are traditional iron tsuba, taking inspiration but not form from nanban work (proportions, seppa-dai and this tsuba's mimi [rim] being traditional), and exhibit strikingly comparable workmanship including sparse gold details on at least a few eyes of the monkeys. Both also have symmetric hitsu-ana suggestive of the Shoami tsuba movement. The remaining cited examples are nanban work from which the motif derived.
The present, unsigned example may be earlier than the cited examples owing to the prominent mimi consistent with the tradition of katchushi (armorer) tsuba from which the Shoami movement evolved. Later generations were also more likely to sign comparable works. I would characterize this tsuba as early Hizen Yagami Mitsuhiro work in the Shoami tradition and probably the same "Shoyoken Mitsuhiro", as the Boston museum example, or possibly a preceding generation or contemporary. It is reasonable that creative Shoami artists could be expected to pick up influences including from extant nanban work. Hizen province generally being a center for foreign trade, and Yagami specifically being a district of the Nagasaki trade port, further supports this.
An article by Robert Burawoy in Bushido magazine, V3,No1, 3rd quarter 1981, touches on the three generations known to have signed Yagami Mitsuhiro. Some reference is made to economy of simpler execution of the mimi by the first generation - with repetitive pattern in contrast to varied detail by the second generation. The thick, prominent mimi of the present example also provides economy of execution as does the second, nanban example in the Walters (though the present example is clearly by a Japanese artisan while the same cannot be said of the Walters’ unsigned nanban manner tsuba).
Good condition. Height, 3 inches. Width, 2 3/4 inches. (Seppa-dai about an 1/8 inch thick. Mimi a little more than 1/8 inch thick. The monkeys decoration a little less than 1/8 inch thick.)