From Renzetti:

"The Presentation True Rotary 4000 Vise is perfect if your tying needs require a variety of hook styles and sizes. Its versatility is unmatched. The Presentation 4000 True Rotary Vise has two rotary tension adjustments. You can use one adjustment to preset a desired level of tension for your basic tying needs. The second adjustment is used for adding tension or holding the rotary shaft in a particular desired position. To utilize the custom features of this vise it must be ordered for the Right (R) or Left (L) hand tyer. Hook range is specified for you to enjoy the True Rotary feature this vise offers."