Iain,
Thank you for your confident identification of this piece and its features. Do you find the manner in which the blade curves is typical for these swords? To my eye the curvature seems to start well below the hilt. The
guom that I have seen and handled had blades with less prominent curvature which extended the length of the blade.
Rob,
You raise an interesting question about whether this copper feature below the guard is related to a Japanese
habaki or to a Chinese
tunkou. The somewhat open-mouthed appearance on this sword is perhaps suggestive of a Chinese influence. However, Japanese presence in Thailand and Vietnam dates as far back as the 15th and 16th C when Japanese mercenaries first appeared in Thailand. Later they took to piracy, and were prevalent also in Vietnam. Guards on Vietnamese sabers in the north and south sometimes resembled Japanese
tsubas, even down to two holes for the utility knives found on Japanes swords (but absent on the Vietnamese ones).
The Cochin dai dao from southern Vietnam also have a habaki or collar at the forte as do Japanese swords. Sometimes, oval serrated washers like Japanese seppa are also found between the guard and collar.
Scott Rodell, a noted expert on Chinese and Vietnamese swords and sometimes contributor to this Forum, has written a nice piece on Vietnamese swords and the influences from Chinese, Thai, and Japanese sources. It can be found here.