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What a truly rotating vise is and why it matters
1) The axis of rotation has to be the same as or very close to the axis of the hook shank.
2) The hook has to be able to turn 360+ degrees without steps.
The very popular Regal vice in the most common position - rotary, but not truly so according to the rules outlined here.
3) The hook must be able to turn in both directions - clockwise and counterclockwise.
Other demands could be that the rotating part of the vice apart from running smoothly without stops or jerks should have a locking mechanism that can lock it in any position. It is also convenient if there is enough space behind the hook for your hands and the materials you want to tie in. Too little space here will make attatchment of tails, tags/buts, hackles, ribbing etc. more cumbersome than needed.
Friction in the rotating part is desirable, unless you use some very special techniques. It takes very little friction to keep the hook steady when you pull on thread or materials, but a totally frictionless rotation - such as those with ball bearings - will probably 'give' in some situations. Ideally the friction is freely adjustable from very loose to completely locked.