The Hook & Hackle Gauge gives you the benefit of two gauges in one. Slide gauge onto vise stem above c-clamp. Gauge may be rotated to back side of vise when not in use.
If you have any doubts about the size of your hooks, simply match to the corresponding number on the gauge those numbers are based on 94840 dry fly hooks.
The hackle portion is easy to use; simply bend hackle around pin and read scale.