Dr. Slick Jumbo Bobbin Threader, w/Half Hitch Tool,Dr. Slick’s aluminum and brass Jumbo tools are easy to see, easy to grab, won’t roll around on your bench and are a pleasure to use. Use this Threader to pull your thread through the bobbin tube – pretty simple, but this one is actually cool and easy to use, plus it gives you another tool to execute a half hitch finish on your fly. The handle is 10mm in diameter.