These feet are for the bottom of your printrbot sipmle. They are great for leveling out the printrbot. If the zipties on your printer make the printer unstable, then use these to even out the base!
I printed mine at 95% size. and had great results!
Footer 1 is for the front. Footer 2 is for the back, as the back is a little larger.
I had to drill/cut out a little spot on mine for the bottom screw where you attach the Printrboard.