Ferrule /(fĕr"rĭl [or] fĕr"rụl; 277)/

Fer·rule

Ferrule

n.
  1. A ring or cap of metal put round a cane, tool, handle, or other similar object, to strengthen it, or prevent splitting and wearing.
  2. Any of various circular or cylindrical metal objects used at joints in a tube, pipe, or rod, especially to assist making a tight seal at a joint. (Machinery)
  3. A bushing for expanding the end of a flue to fasten it tightly in the tube plate, or for partly filling up its mouth. (Steam Boilers)
  4. A bushing used at the joints of metal tubing in HPLC equipment to make a tight seal. (Chemistry)
  5. One of several small rings at the top of a casting rod which holds the fishing line. (Fishing)