To prevent the slippery of blade from scabbard, there were "Habaki-tome" in old days. In the case of gunto, during marching or fast movement in battle, more safe blade holding methods were needed (espeically in army). They are "Chyuoha-tome" (Stopper) made of metal and "Button-tome" made of leather.

Army : Early version used stopper style, middle version used stopper and habaki-tome, later version mainly used button style with leather scabbard and habaki-tome.

Navy : Mostly habaki-tome and stopper style is rare. This is due to different environment condition compared to army.
 

Stopper style
 

The location of stopper is different for each swords.  It's so delicate that if button hole or length doesn't match, it's doesn't work. In the case of army, stopper end is hung on the hole in iron saya, hidden in kuchi-gane. Int the case of navy, stopper end is hung on kuchi-gane itself.

Button style

Ko-seppa unified style leather button

Fuchi-maki style leather button

=> Tassel