This is a remix of Steve Medwin's awesome Customizable Straight Beam for LEGO Technic.
I added the ability to make it half-height or to have "plus"-shaped holes and cleaned up the code a bit. With these modifications you can make pieces that fit on the plus-shaped axles. To specify the number and shape of the holes in Customizer, use a string with +'s and o's. For example, the string "+ooo+" for a block with five holes: pluses at the ends and three round holes in the middle.
I originally made the half-height +o+ version of this as this thing, before finding the customizable one and re-writing it around that design.
As an additional feature, use a capital O for a sideways hole and a capital P for a sideways plus-shaped hole, although they probably won't print as well on most home printers.
If you make a customized one of these in Customizer, please name it descriptively.
Edit v3: You can use an "x" for a blank segment with no hole. Also cleaned up display in quick render mode by adding an extra 0.05 millimeter to the holes.