The feet serve mainly to anchor the Viton bands that tension the actuators, but if you are not using a stand (we reccommend that you do) they also serve to support the microscope. You need two tilted feet and one untilted foot, as provided in feet.stl. In some circumstances you may need to use taller feet, as provided in feet_tall.stl but this is now deprecated, in favour of using a microscope stand (which means you don’t need the tall feet).