Digital Tachometer showing RPM.
can be connected to most rotary tools, like drills, lathes and mills.
The digital display is available on eBay with sensor.
the bearings used are 6000RS and 6001RS
M6 bolt in the end.
a small round 4mm magnet fits the chopper wheel
I used a common 2.1mm 12volt connector, it could have a cord to supply power.