I use a small pair of internal calipers and a hand held imperial micrometer (more sensitive than any vernier) also I'm looking for any ovality ie out of round. This is an interesting example of how the toolmaker / machinist has to be 'on the ball'. The internal diameter of the tube measures 0.5615 inch max when examining a batch of machined tubes, ie one and a half thou up on five hundred and sixty thou (imperial). The bottom cover is an interference ie press fit into the tube and has a contour drilled hole to accept the lower part of the bob with minimum rattle. I use it to press the polished / buffed tube onto the bottom cover as well as stamping my logo onto other finished product ie 'Richard Kell Made in England' as on my dovetail markers and centre finder. An excellent piece of equipment that I bought from a Northampton machinery dealer 200 miles away when I first became self employed in 1983. The fit and function of the hand scraped slideways of the ram are still glassy with no metal pick up.

The above is at the smaller of my two flypresses, a no.1 Denbigh, somewhere 1900 /20 vintage pressing the plumb bob tube onto the bottom cover. And not the first time this has happened. Yet it does not have my handmade approach.flattery indeed. so I stupidly discontinued the plumb bob somewhere around 1990 and hey presto a clone soon sprang up.

I first produced these plumb bobs around 1984 and I made quite a few until being too busy with tooling for electronic circuit board assembly. The above is my solid brass plumb bob in matching fitted brass case.

Small plumb bob