This is a compact tramming gauge housing for a desktop sized CNC router/mill. This uses 1.6" faced dial indicators (AGD Group 1). Specifically, this tool was designed for this dial indicator from Amazon: https://www.amazon.com/gp/product/B01BHHXGEG You have to remove the backs from the indicators before inserting them into the tramming tool.

For these cheaper dial indicators, if you buy two of them, they may not be calibrated closely enough to function as tramming indicators. For mine, I had to insert shims under the top cap of one until the stems of both indicators were the same length while at rest.

The hole in the top is designed for a 1/4-20 bolt thread to be tapped into and then I cut off the head of 1/4-20 x 3" bolt and threaded it into the top of the gauge to use as the shank. You could probably use a 6mm bolt the same way. The holes on the clamping surfaces on the outside edge of the gauge are set for 3mm screws with the bottom holes slightly enlarged for use with threaded inserts.

This Thing was a heavily modified version of https://www.thingiverse.com/thing:1688277 so I credited the maker of that thing with a remix. Thanks for that!

The example I printed from this STL was printed in Black Amazon Basics PETG with a .6 mm nozzle at 400 micron with 100% infill and it printed quite nicely. Print it laying on its back with full supports to keep the screw holes open.