Pulled this off their FAQ page

Question: How do I determine the correct dimensions for mounting my Norvise?

There is (or was) a drawing with your vise showing a recommended distance of 14" to 18" for the mounting holes about 1" in from the front edge of your board or table. Some commercial fly tyers will have several mounting holes for optimal spacing depending on what they will be tying at the time. I like mine 16" apart.

Hope this helps.

Regards,
Scott