thimble -
A ring of metal or rope used in a ship's rigging; it is a protection against chafing.
Wikipedia
A thimble is a small hard pitted cup worn for protection on the finger that pushes the needle in sewing. The earliest known thimble was Roman and was found at Pompeii. Made of bronze, its creation has been dated to the 1st century AD.
OmegaWiki Dictionary
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thimble A pitted, now usually metal, cap for the fingers, used in sewing to push the needle.