How to adjust the fit of a saya (scabbard/sheathe)

The saya, or sheathe, of a Japanese sword is made from wood, and because wood is an organic product it is susceptible to shrinking or expanding slightly when encountering different atmospheric conditions.

Because modern day production swords are often quite new and it is not practical to season the wood over time before shipping, it may occur that a katana whose saya fitted well when it was shipped may arrive slightly tight or slightly looser than what is ideal. This is especially common in the hotter/colder months, but is a relatively easy fix either way.

If the saya is hard to draw and is too tight, you can either simply spend some time drawing and resheathing it until the tighter wood wears away naturally and give it some time to adjust to an atmospheric change. Alternatively, you can take a small file and gently and carefully remove a little of the wood from the inside of the "koiguchi" - the "mouth" or opening of the sheathe and keep checking until it achieves the ideal fit.

If the saya is too loose, you will probably want to "shim" it. Because this issue is so common on production swords, one of the leading sword manufacturers - Paul Chen's Hanwei Forge - used to include an instruction sheet on how to shim their swords with every sword they sold. Nowdays, the instructions are online, but below have been reproduced for your convenience.

How to Shim a Saya

1) Thoroughly degrease the throat of the scabbard to a depth of approximately 1 inch from the entrance. This can be easily done using cotton swabs and a solvent such as lighter fluid or paint thinner. Allow the solvent to completely evaporate. Do not allow the solvent to contact the lacquer finish on the outside of the scabbard. (Showing as Fig 1)

2) Take a section of wooden shim approximately one inch square from the shim in your Maintenance Kit (CAS reference OH1003). If you do not have a Maintenance Kit, a similarly sized piece of wood veneer (available in rolls from lumber yards or home stores) will work. Try this shim for fit in the top of the throat of the scabbard by pulling the sword about an inch out of the scabbard and placing the piece of shim on the habaki (the brass ferrule which butts against the guard). The piece of shim should be slightly narrower than the side of the habaki. Gently guide the shim into the throat of the scabbard while resheathing the sword. You will probably find that the fit is now sufficiently tight. (Showing as Fig 2 and Fig 3)

3) Remove the sword and the piece of shim from the scabbard. Apply a light coating of glue (such as Elmers) to one side of the shim and replace it in the top of the throat of the scabbard, so that the shim is glued to the wood and the top of the shim follows the top of the throat. Make sure that the other side of the shim is dry and completely free from glue and that there is no excess glue elsewhere in the scabbard throat. (Showing as Fig 4 and Fig 5)

4) Gently slide the sword into the sheath until a 1/8-inch gap is left between the top of the sheath and the guard, being careful not to move the shim. (Showing as Fig 6)

5) Allow the glue to dry and remove the sword. Make sure no excess glue is visible in the throat and then gently resheath the sword until it is fully seated. (Show as Fig 7)

6) If the sword is still loose in the scabbard, repeat the same treatment on the other side of the throat (this is unlikely and the other side of the throat is more likely to be used for a second refitting if and when the sword fit becomes loose again). (Showing as Fig 8)

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