Herter's Hook Sneller
I cannot lay my hands on the instructions for the Herter's Hook Sneller at this time.
Here is the information from my 1973 Herter's catalog.
By reading the info and looking at the picture you cant in all likelihood be able to figure it out.
As you can see it was designed to be used on a Herter's or Thompson type fly tying vise.
Hope this helps!