Hi

I am in the process of making a fly tying vice, the design of the jaws is a little like a small toolmakers clamp, twin screws with opposing forces. My design will use left and right hand pitch threads for the front screw with the adjuster wheel mounted between the jaw plates pulling the two jaw plates together to lightly clamp the hook in place. I will be incorporating a cam at the rear screw location to give a fast acting tension cam forcing the rear of the jaw plates apart.

My question is should I use 24 tpi, 32 tpi (M5 metric) or 36 tpi (M4 metric) for the front fine tension screw?

The jaw plates will be approximately 12mm high and about 1/4" thick near the front tension screw location, possibly slightly thinner once fully machined.

Ideally there should be a little slop in the threads to allow a little movement in the front tension screw assembly to allow the tip of the jaws to move sufficiently to lightly hold the hook before binding up.

I was going to try 10 X 24 OR 12 X 24 UNC for the front screw or M5 x 0.8 or M4 x 0.7?

Any ideas on the best option?before I order expensive taps from the USA?

The jaws will be made from 01 carbon steel (ground flat stock) or D2.

Thanks in advance for any advice.

Kevin.