The .3mf file contains 3 plates so that it's easier to print the ID and OD gauges in different colors if you want. If you want them all the same color, just use the one plate that contains all of the gauges.
The author remixed this model.
The numbers printed on the original model represent the difference between the standard ID (8mm) and OD (22mm) of a 608 ball bearing.
I'm a simple-minded guy so I prefer to have the actual modeled dimension on the gauge so that when I'm designing a part I don't have to do any math; I can just look at the number on the gauge and model my part to be that size.