The Menuki has its origins as a cover for mekugi pegs, on tachi koshirae. With the advent of the katana, the koshirae mounting techniqu
es evolved to eventually the state we have today. In any case, the menuki can be a rather interesting topic, as iaidokas perusing the options for their iaito may resonate with.
Menuki comes in pairs, and each one would be affixed on the ura (back side when iaito is sheathed, "faces" towards the body when iaito is worn) and the omote side (front side when iaito is sheathed) of the tsuka. The usual placement is top left side (omote), and bottom right side (ura) - this may differ (i.e. centered-menuki on both sides of tsuka, or reverse positions, and is beyond the scope of this article).
Partially concealed by the tsuka-ito (handle wrapping), in the case of the hineri-style tsuka maki wrapping, some might be tempted to pry the tsuka-ito to have a better view... Please do not do that, as the integrity of the tsuka ito concerns safety.
Like the other koshirae, artisans draw inspiration from nature, daily life & the esoteric for menuki designs. Careful planning is done by the artisan to ensure the menuki are correctly positioned.
Regarding the placement of the menuki on the tsuka, in the case of menuki with geometric designs (e.g. mon), the relative direction and positioning may not be apparent. However, it should be easier to discern in the case of flora or fauna-related designs. The general direction of the stem, head (when turned)/body is generally in the direction of the fuchi-gane.
First: Ken katabami menuki
Second & Third: (
Top: Paired menuki, notice the turning of the head
Bottom: Hawk on Pine tree, Ura-side; head (unturned) towards fuchi-gane.)
Fourth: Breaking waves. (Top: Omote-side, Bottom: Ura-side)