I like to keep my tools in peak condition, and the corners of combination squares are begging to be dinged. These caps help protect the corners when ruler isn't in use.

NOTE!!: I didn't model the threads. Rather, I printed with a proper pilot hole for M6x1.0 and cut the threads with tap and die to try out the workflow. If you want threads modeled, drop a comment and I'll create those too.

In slicer, I have set supports to be on build plate only for the cap_base with the closed end on the plate and open end facing up. Printing in this orientation reduces the chance of layers splitting when tapping. The cap_screw was printed with knob face on build plate which isn't ideal, but as long as you are careful when cutting threads you should be fine. 

For cutting threads in cap_base, just tap like normal. Make sure to back-out often to cut up the chips.

For cap_screw, it is a little trickier. Dies on one side have a lead-in and other side is the final thread dimension. Start the thread as normal with lead-in side and go until you have cut deep enough on the first few threads. Then, flip the die to cut remaining threads while being careful not to stress the shank too much to the point of shearing.