I can well appreciate David's experimenting with different ideas and styles of measuring instruments - good ideas are worth playing with and David's prototype is very interesting.

I've been less daring and stuck with a more conventional design:





with the ball brazed to the end of the rod. I also made a wooden case that holds this and two bore-gauges and I can take them to gun shows. Portability is a big "plus" and I've never been refused permission to measure wall thickness or bore at any show.

Altho I usually use the device hand-held and horizontal, I can clamp the block in a vise with the rods vertical and lower the barrels over the ball-end. Never tried suspending it.