The grooves (Hi)
Here is an article about grooves (Hi)
This point to come back to a widely spread myth : no, the grooves were never made to make easier the blood flow on the blades !

In fact, at the beginning, they appeared for aesthetic reasons. But soon, when the sabers got thicker and heavier, it was thought to be useful to reduce the weight of the sabers and to bring closer the balance point of the tsuka.
Therefore the gain was double in terms of handling. However the grooves stayed as a minority, since on a Shinogi structure, for example, they limit very much the structural utility of the Shinogi (longitudinal edge) .

Consequently the blade, although with the same thickness, may warp easier in case of strong unintentional impact on the flat of the blade. For this reason, even nowadays, non-grooved blades are preferred for cutting. But sometimes the grooves have also another utility, not so noble, for example in order to cancel a flaw on a blade. Then, we are speaking about Atobi or Atobori. They also cause worse injuries.
Types of grooves:
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Bo-hi (or Bo-bi) : wide grooves along the entire length of the blade, also called Shinogi Hi when the Shinogi constitutes the lower edge of the blade.
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Koshi Hi: partial wide throats
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Futa suji Hi : narrow grooves along the entire length of the blade.
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Gomabashi: partial narrow gorges

Bohi no tsure Hi/no soe Hi : composed of a wide groove and a narrow groove. The thin
groove is at the end of the wide groove in the tsure Hi version.
Vocabulary about grooves :

Tome : where the groove starts, may be Kaki-toshi (all along the nakago), Kaki-nagashi (up to half of the nakago), Maru dome (rounded beginning at 0.78"-1.18" on the nakago) or Kaku dome (square beginning at 0.78"-1.18" on the nakago). Hisaki agaru : groove that spreads significantly beyond the yokote. Hisaki sagaru : groove that stops at the level of the yokote.
Chiri : chamfer

Katana and etiquette :

The etiquette is very important all along the life of a samurai. Wearing a katana or saber subjects to some rules (referred in an article of the blog : wearing a katana), but a lot of other standards have to be observed. If you are fair enough, you have to know that presenting your saber to someone must follow
specific steps. If the saber is in its saya (sheath), you should present it horizontally, sharp edge towards you,
to show that you are well-meaning. The tsuka is at right as shown at the picture below.
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If you present the katana without saya, you have to hold it vertically, sharp edge towards you, and with both hands so that you give enough space to the other person to grip the saber. (the etiquette allows to set up safety rules).
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At that time there were a lot of other rules. the carrying of katana could be changed, edge downwards to show your neutrality while the edge upwards meant a protective attitude. Depending on the situation, the classic wearing of the edge upwards could be different.

When a samurai entered a friend or a high-ranking nobleman's house, a tea house, in a theater or in the Geisha district, the katana and the wakizashi were to be left in a rack at the entrance hall. With a not so close guest, a samurai had to put his katana on the ground, before kneeling
on the tatami. The katana was put on the right, to not draw it easily and so you meant that you were friendly with your host. If the katana was placed on the left it was not a fault but it meant that the samurai was suspicious or vindictive. The wakizashi was kept in the obi because it
was not disturbing when kneeling.

Something else, the saber were to be on your left or right but the tsuka (grip) towards yourself. Otherwise the stuka towards somebody else meant that the samurai thought the person was too clumsy to cease the katana and use it. And it was a lack of consideration, very impolite.

It was forbidden to touch somebody else's saber without his explicit permission. Some fights might occur as somebody had touched unintentionally a samurai's saber, for example in a crowded street.

The tsubas (guards), vocabulary and shapes

Sometimes we are asked if some forms of tsuba are more traditional than others. In fact, there have been always a lot of tsubas, and their irregular shapes were specifically named. Nevertheless, the most common tsubas were as Maru gata (round), Nagamaru, or Mokko gata.

Here are the most usually met forms :
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But the vocabulary about tsubas is much more complex. In fact a tsuba may have many elements, for example several holes having an especial shape for a specific utility.

Here is a picture to explicit the basic vocabulary about tsuba :
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鍔 (鐔) Tsuba : guard.

形 (型) Gata (Kata): Shape of the tsuba.

平 Hira : Surface of the tsuba.

耳 Mimi : edge of the tsuba.

中心 穴 Nakago-ana :
the hole through which the tang passes (tang: part of the tsuka).

櫃 穴 Hitsu (-bitsu) -ana :
Holes to place Kogai (right) and Kozuka (left) So it is specified : Kozuka hitsu ana, Kogai histu ana, therefore a Hitsu ana can be for one or the other. A Kozuka is a small knife, which fit in the saya and the grip of which goes through this hole in the tsuba.

地 金 (心 鉄) Jigane (Shingane) :
Metal used for the tsuba.

責 金 Sekigane :
Piece of material (often copper) placed at the level of the Nakago ana to adjust the tsuba to the blade to avoid loose.

埋 Ume or 当 金 Ategane :
Piece of metal placed in the Kozuka or in the Kogai ana to fill it.

覆 輪 Fukurin :
An additional outward edge, often in soft metal (such as gold) . Quite rare.

鏨 跡 Tagane Ato :
Traces made when adapting the tsuba to the blade (sanding).

銘 Mei :
Eventual craftsman's signature, usually near the Nakago-ana.

切 羽 台 Seppa Dai :
It is a flat base on each side of the tsuba, which is often over-raised and receives the seppas.

腕 貫 穴 Udenuki ana :
Two small holes to pass a string.

透 鍔 Sukashi tsuba :
Tsuba made of an openwork iron.

But there are other things to be considered about the shape of a tsuba, beyond its outlines, in particular the edges (Mimi). They can have different shapes as shown on this picture :
japan tsuba custom katanas