Renzetti uses rubies to ensure lasting wear and eliminate the constant cut of thread as ceramic or other products in the market. The unique tapered protrusion insures maximum thread spool retention and the bobbins ruby tip will keep the thread moving smoothly and wont allow your fly tying thread to cut into the bobbin tube. The tube length of the Renzetti Saltwater Bobbin is 2.75″ and the diameter is 1/8″.