D'après ce qui est souvent dit, les Mekugis sont des chevilles en bois qui sont utilisées pour fixer la lame à la poignée du Katana.
In reality it is more of a security, because the whole nomenclature is already very well fixed, moreover with the pressure that your hand exerts on the handle it strengthens the whole. One Mekugi can be enough, but traditionally there will always be the two wooden pegs.
These Mekugis are traditionally made from bamboo. These small wooden pegs can easily wear out with use, so you may have to change them. Some people opt for DIY by making these little pieces themselves.
You can also find more solid ones easily on the internet