I'm sure most of you all know that the guard of a Japanese sword is known as the tsuba. They are available in various sizes and shapes and this really small tsuba is known as a hamidashi tsuba. Since tanto were carried in the obi (sash), a full size tsuba is very uncomfortable, especially when having a katana inserted as well. Most tanto are in kaiken (really small dagger), aikuchi (without tsuba) or with hamidashi tsuba.
Though there have been example of small tsuba on tanto as well, they are outnumbered by far with one of the tanto koshirae types as described above.
Anyway, the just-overlapping hamidashi tsuba is almost exclusively used on tanto. It's tiny almost bevel-like shape raises an often asked question about the true use of the tsuba on a Japanese sword.
While the initial thought of many will be is that the tsuba is a sword guard - meant to protect the hands from an opponents strike - it is in fact the opposite.
The tsuba indeed protects the hands... from slipping over the sharp cutting/slicing edge of the sword.
In great contradiction to most European swords, the Japanese sword is truly razor sharp. Without a stopping bevel chances are that your hand slips while thrusting the blade into an opponents... ouch.
When looking at historic facts the tsuba's actual use is more or less proven: cutting marks caused by swords on tsuba are quite rare. In contrary to cutting marks on western sword guards.
To go back to the tanto in the picture: the hamidashi tsuba is most likely made out of shibuichi and has a golden inlay depicting an ogi (paper hand fan). Also it has openings for the kozuka (utility knife) and kogai (hair pin and ear-cleaner) to pass through. Truly exquisite work!