I want to replace the horizontal clamping screw in the mini vise with a knob that’s easy to tighten by hand without a hex tool (something like shown in the photo). What is the diameter and thread on that screw?
http://ecx.images-amazon.com/images/I/51FBHdbRDZL.SL1181.jpg
You sir need one of these and a tap set 
It’s an M6 if I’ve measured correctly—I don’t have my tap set on hand as it’s currently buried in my garage somewhere (we’ve been doing a renovation this summer).
McMaster has a few like this but the head diameter on that is a bit large—might be hard to fit your fingers in around it.
We use Metric threaded hardware throughout the Nomad Machine.
And Yes, that specific thread on the Vise is M6 x 1 pitch, which is the standard M6 thread.
Yes I figured out that I need one of those measuring kits 
Thanks for the tips UnionNine and Apollo!
See now I would have thought buying a machine from the US it would have had all imperial threads, but it has metric like we use here. It’s awesome!!