Bobbin Holders are a personal choice for what feels comfortable in your hand. These days there are also ceramic heads which aid when tying smaller patterns with finer denier silk.
Essentially the bobbins job is to deliver silk to the hook to dress the fly. The bobbin should feel comfortable in your hand and add enough weight to keep the silk tight and hold the dressing in place mid tie.
Take a look at our range of Bobbin Holders, and see which one best fits in your hand.