At 3 mm x 2.5 mm, the "stapes" in the middle ear is the smallest named bone in the human body.
The shape of a stirrup, this bone is one of three in the middle ear, collectively known as the ossicles.
The ossicles convey sound pressure waves from the outer ear (and ear drum) to the inner ear, where the waves are translated into nerve impulses that go to the brain for identification.
The other two ossicles are the malleus (hammer) and the incus (anvil).