The keycap mount refers to the molded plastic piece on the underside of each keycap that allows it to attach to the keyboard switch. The shape and spacing of the mount needs to precisely match the stem of the switch in order for the keycap to fit properly.
For larger keycaps like spacebars or enter keys, there may be two or more mount points to provide stability across the width of the key. The spacing between these multiple mounts is critical - keycaps are designed for specific keyboard layouts and switch spacings.
Download our guide to mount styles for an illustrated look at our mounts and the key switches they fit.