Shimming the Koiguchi For a Better Fit

A loose fitting saya is pretty common, especially with the one-size-fits-all production saya and while this is annoying it can also be dangerous, as well as a way to potentially damage your sword. The fit of the habaki inside the koiguchi should be firm so the sword doesn’t fall out on it’s own but not too tight where it’s difficult to remove it. Too much pressure can cause damage to the saya, especially on the inside walls of the koiguchi as this can eventually lead to the saya splitting or cracking at the seams located on the ha and mune. Koiguchi fit is considered standard user maintenance and should be something you learn to do yourself. Adjustments might be needed several times throughout the life of your sword depending on use and in some climates where there are very cold or hot months or where humidity levels increase and decrease, causing the wood of the saya to contract and expand.

This is a simple way to adjust the fit of your saya’s koiguchi. You will need a shimming material such as a thin wood veneer. Paper can be used in place of wood but I prefer wood since it can easily be filed if you need to loosen the fit. You will also need a glue such as a wood glue or general craft glue, avoiding glues that have harsh chemicals or become hard and brittle, such as cyanoacrylates. You’ll need a pair of scissors or utility knife to cut the shim material. A pen or pencil to mark the length you’ll need and I like to use a simple wood tool to help press down the glued shim since my fingers don’t quite fit inside the opening.

Please watch this basic koiguchi shimming video for more instruction