This is the center insert for a Happ style arcade button. I designed this so that text or indicators can be added to the tops of buttons, or so the color of a button may changed. I print it solid as most of it is hollow anyway. There is a slight concave recess on the button top. This is for the long Happ style buttons that are about 44mm from the top of the button to the bottom of the threaded portion of the button housing.