Bobbins are the critical tool in tying since they must keep smooth tension on the thread spool and have super smooth inserts to apply the thread to your fly.This bobbin fearturesDelrin feet for smooth tension on the thread spool, and a ceramic insert for smooth thread application. These funnel shaped inserts allow for a smoother application of thread or other materials as the bobbin is rotated, and they cause less breakage than traditional pipe or straight edged inserts.