Thumb nuts.

Thumb nuts are oversized threaded nuts designed to be finger-tightened and are usually knurled. Most of us will have used them at some time, they're usually found on pairs of compasses for example where they're used to hold the lead/point in place. For a project I needed an 8BA thumb nut, and being unable to find one online I decided to make my own.

I had a rough idea of the size wanted, and started by milling 8 flats on a length of 1/2" brass bar;

For this I used a dividing head. I cut flats as I wanted to be able to tighten the nut with my fingers but I dislike knurling, I never enjoyed knurling when I worked as a turner and I feel that it can put undue stress on a small lathes like my Unimats.

I just cut what looked right, in fact the measurement across the flat is 12mm but that was just by chance.

Once the milling was done the bar was finished by turning a step front and back and drilling and tapping 8BA;

There's also a recess turned in the centre, this is so the clamping force is concentrated around the outer face where there's more friction.

The finished nuts (I made a spare);

Don't they look smart!

Paul.