This is a PTFE tube cutter with measurement scale for short pieces to put in a Creality Hot End or a Prusa Mini. You slide in the PTFE up to a specific length and then cut it. Or slide a long section in and it's held at both ends so you can get a clean straight cut.
I use an exacto knife to cut the tubing in the slot but you can use any razor blade as well.
It's also 100 mm long so you can use it to mark filament when testing for E-Step calibration of the Extruder.
You can also print this in 2-Colors to make it easier to read the numbers. There are two files; a top section and a bottom section. You can find them here: Two-Color Top Section: https://bit.ly/3jOk8E7 Two-Color Bottom Section: https://bit.ly/3xBw3Kw
More details are here: https://youtu.be/pQlZoMF0CVE