Something to make a mark or check an angle quickly. I sanded the side where the bar mounts to make sure it sets in the slot squarely. I first printed with white for several layers, switching to a darker color until after 5.2mm layer, switching back to white to give contrast for numbers.

There are two different bars, one for any 3mm screw and the other for 3mm countersunk. General settings for printing. 3mm threads are formed in print.