A quarter.
in the eye socket on the head
The eye sockets of the head
The eye sockets of the head
The letter is I. Eyes are part of the head.
On its head obviously!
in the head
what is this knot over my eye on my forehead
The riddle describes two objects: a needle (which has a "head" but no eye) and a potato (which has an "eye" but no head). The phrase "half of the answer upon a thread" suggests that the answer relates to sewing, where a needle is used with thread. Therefore, the answer is "needle and potato."
The area on a bird's head between the eye and beak is called the lores.
An elephants eye is 34 millimeters in diameter. The elephants eye is relatively small compared to the size of its head.
eye
no