Katana Koiguchi everything you need to know about this part on a Katana


Everything You Need To Know About Koiguchi

The Koiguchi, an integral part of the Japanese katana, is one of the reasons wh a katana fits into its sheath (saya) so firmly.  If you're interested in finding out more about this special component, keep reading!

What Is Koiguchi?

The Koiguchi refers to the section of a Japanese Saya or sheath that fits snugly around the Habaki and secures the blade in place. A properly strengthened Saya will stop the Katana from slicing through the Saya when quickly drawing it.

The opening of the Saya is called Koiguchi. Due to its shape, the Japanese name translates to "mouth of a carp". Also known as the "mouth of the Saya," the Katana Koiguchi is usually constructed from buffalo horn.

To fit the Katana precisely and prevent the blade from repeatedly cutting the Saya, a Koiguchi must be meticulously crafted. The outside of the Koiguchi is typically covered with another "cap" made of brass or horn in order to better protect the blade.

What's The Usage Of Koiguchi?

The Koiguchi is the sheath's opening, where the sword is placed. If you plan to practice any drawing techniques, Koiguchi helps prevent the sharp blade of your Katana from cutting cleanly through your Saya.

Swords with properly fitted Koiguchis can be stored upside down in their Saya without fear of falling out. At the same time, you can draw them just as quickly with a quick press of your thumb on the Tsuba, aka the hand guard. Thus, Koiguchi essentially helps you practice your quick blade drawing skills. 

What Are The Common Lengths Of Koiguchi?

The size of a Koiguchi varies depending on the Katana. However, typically, the length of the average Katana Koiguchi are usually 4-6 cm.

Ideally, the Koiguchi would be reinforced such that the blade wouldn't sever the Saya when being quickly drawn. The Koiguchi should be tight enough so that when the sword is sheathed correctly in its Saya, it can be turned upside down without coming out. Yet you should be able to draw it quickly by pressing your thumb on the Tsuba or hand guard.

Frequently Asked Questions

  1. How Much Does Koiguchi Typically Cost? 

Ans: It's common for a Buffalo Horn Koiguchi which is quite inexpensive. It can cost between a couple hundred dollars. Non-reinforced varieties are naturally just a standard feature of the sheath and don't demand any extra payment.

  1. Why Has My Koiguchi Become Loose? 

Ans: On rare occasions, the traditional glues made of pine or rice used to attach the Koiguchi to the Saya fail owing to climatic conditions. You can reattach them and fasten them in place with some wood glue. You can also use gorilla glue to secure it even better.

The Koiguchi and habaki of the blade must fit together precisely; otherwise, the Koiguchi may slip out of the Saya, be challenging to unsheath and draw, or rattle. Unlike custom-made katana, common swords are made on a 'nearest fit' basis, so the Saya mouth may need to be slightly shimmed or filed to provide a snug fit.

In addition, the inside lining of the sheath's mouth will wear out and need replacing if you often draw the sword from it or leave it removed for long periods. All Japanese sword owners need to maintain them from time to time. 


Not many are well aware of a Japanese Katana's unique components, and believe me when I say there are many! For all the curious folks, I share all about Katana Koiguchi in this article, if you want to learn more about other katana parts please check this guide.

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