Made for 9.5MM Dial Indicator shaft.
Dial Indicator (On Amazon)
Digital
Clockwise Tools DIGR-0105 Electronic Digital Dial Indicator Gage Gauge Inch/Metric Conversion 0-1 Inch/25.4 mm with Back Lug Auto Off Featured Measuring Tool

Analog(My Favorite)
Clockwise Tools DICR-0105 Dial Indicator Gage Gauge 0-1 inch Measuring Tool

1)Home Printer
2)Turn off printer
3)Use paper to gap hotend in the center of print-bed, lookup bed leveling if this is not familiar concept.
4)Zero Dial Indicator or remember the number
5)Move dial indicator to the corners of heated and set to the same number or zero position on dial indicator by twisting the bed screws.
6)Recheck center and corners and verify the gap with paper pull under hot end.

*WATCH THE DISTANCE BETWEEN YOUR PRINTER FRAME AND THIS MOUNT*

*Note best results are with a hot hot-end and a hot hot-bed to truly measure the gap without filament getting in the way.

**If you hear clicking in your extruder you are too close to the bed or not running your filament hot enough

***If your filment is not sticking and you have a clean bed then it is bed height most likely.

This object was made in Tinkercad. Edit it online https://www.tinkercad.com/things/i3eZZHiHK2j