This is a simple set of calipers, used for taking measurments.

I use them formaking cosplay helmets and such for my kids.

Set the tip of the blades on either side of the object you want to measure. Then hold the tips (without moving them) agains a ruler and you'll have you measurement.

You will notice that the STL only has one blade. All you need to do is print it twice. It's been designed so that all you need to do is flip one and put an screw and nut throught the joint to lock them together.

When you are taking a measur, if you tighten the nut, the calipers will hold theire measur while you hold it agianst the ruller.

Simple but usefull.