Thimble 1 : (1) A u-shaped device inside the eye-splice of a rope or cable. (2) A device that connects a chimney to a roof and allows it to pass through safely; it is used with wood stoves
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}