I was going to add this to the What I Did In The Workshop thread, but having taken a photo, I'm not exactly proud of the workmanship.
I picked up a Moore and Wright electronic "dial" indicator as a good deal off eBay, but it came without a tip.
I had some 4.5mm stainless kicking about, but it's horrible stuff to machine.
The thread is 2.5mm with an 1/8" ball bearing pressed into a 3mm hole in the end, and then rounded over to retain the ball.
I could see the knurling was dodgy, but it was getting late, so I carried on anyway.
Olympus E-M1 Mk2, 60mm macro, MC-2.0 teleconverter + 2 x 10mm extension tubes
15 raw shots, stacked in camera, to give this as a jpg, with no further enhancement or cropping.
At its closest focus distance, the threaded part just about filled the frame.
Bill