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

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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 鯉口?

Koiguchi of Katana

The Koiguchi is the opening of the Katana scabbard. It refers to the section of a Japanese Saya 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 is "鯉口", translated 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 Koiguchi 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. 

The proper way of drawing a katana is to use your left thumb to push the Tsuba up slightly to release the Habaki from the Koiguchi. This move is called "鯉口を切る" in Japanese, literally means  "cut the koiguchi."

Importance of tight Koiguchi:

Given the wear that happens with repeated drawing and sheathing the Katana, the fit of Habaki and Koiguchi is made quite tight at first. Over time, as the Saya  wears down, it will fit perfectly. Don't worry even it get loose, this is easy to fix.

During the Edo period, there were several incidents involving Katana being drawn within castles, such as the famous Matsunoroka (松の廊下) incident from the Chushingura (忠臣蔵). To prevent accidental drawing, some Katana mountings (koshirae, 拵) were designed with safety mechanisms. For example, some koshirae did not allow the blade to be drawn unless the Kodzuka (小柄, small utility knife) was removed first. This demonstrates how much the samurai of that time feared their swords slipping out of the Saya easily.

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. 

Conclusion 

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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