What does "thimble" mean?

Thimble: (Mech.) Any thimble-shaped appendage or fixure. Specifically: -- (a) A tubular piece, generally a strut, through which a bolt or pin passes. (b) A fixed or movable ring, tube, or lining placed in a hole. (c) A tubular cone for expanding a flue; -- called ferrule in England.

Additional senses

  1. 2.(Naut.) A ring of thin metal formed with a grooved circumference so as to fit within an eye-spice, or the like, and protect it from chafing.

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