Superfly Hook & Hackle Gauge helps to quickly measure and select the size of hackle for tying dry flies. To use it, simply select a hackle feather and wrap it around the peg on the Hook & Hackle Gauge. The tip of the hackle fibers will spread out on the series of rings on the gauge and will indicate size of the hackle. The Superfly Hook & Hackle Gauge has a hole on one end to allow it to be placed on the stem of the vice for instant, convenient use.