Metric threaded stem casters are mounted the same way a screw is drilled in. For these casters to be mounted, a hole needs to be pre-drilled into the mounting unit. The stem then needs to be matched up with the hole size and thread count of the pre-drilled hole. This measurement is critical for the caster to be mounted. If the stem size and thread count do not match up with the mounting hole, the caster will not work.