Source: Primary sources
The kankyûtô, written 貫級刀 or 貫首刀 in Japanese, is a small tool with a double-edged tip, made of a single piece of steel. that could be worn in the scabbard of a sword instead of a kozuka.
Their use was associated with the practice of cutting enemy heads and presenting them with a tag, a practice that continued into the Muromachi period (1336-1573). Theories vary about whether it was used to affix the tag, or having to do with adding a thread to a head for mounting or transport.1
A typical late Edo period kankyûtô.
Mandarin Mansion stock 2021.
The design dates back to at least the 11th century but most of them encountered today are from the Edo period.2 In his article, Mike Vinehout mentions another piece offered in Japan, its description mentions that Daimyo Matsudaira Sadanobu (1759-1829 A.D.) had these reproduced by the notable smith Tegarayama Masashige, based on an older piece that was attributed to Minamoto Hachimantaro Yoshiie (1039-1106 A.D.), a notable Heian period samurai. He believes that the wearing of them during the Edo period, long after the tradition of collecting enemy heads ended, was probably an act of nostalgia.3
Other double-edged tools
The kankyûtô looks much like the bashin (馬針) or "horse needle", a horse bloodletting tool. The same characters can also be pronounced umbari which is generally used to describe the same tool, but with a longer blade. Both bashin and umbari are usually not of one-piece construction and lack the hole at the end that kankyûtô always have. According to Markus Sesko, bashin became part of Higo-koshirae (Higo-style sword mounts).4
1. Mike Vinehout, assisted by Markus Sesko and Dr. Chris Leung; The Rituals of Victory. Japanese Sword Society of the United States Journal, 2014.
4. Ibid. and Markus Sesko; Encyclopedia of Japanese Swords. Lulu, 2014. Page 23.