What is Mekugi-ana in Japanese Katana terminology?

The term ""Mekugi-ana"" (目釘穴, めくぎあな) refers to the hole in the tang of a Japanese sword, which is made to secure the blade to the handle by inserting a peg called a ""Mekugi"". Depending on the changes in the style of sword mountings over different periods, the hole may be re-drilled, and older swords often have multiple holes.

To prevent the Mekugi from falling out, some holes are shaped like keyholes or chrysanthemums. The timing of drilling the hole varies depending on the era and the swordsmith. There are various types, including those where the signature is carved avoiding the hole, and those where the hole is drilled over the signature.