Sherline CNC mounting bolt sizes?

Simple question: does anyone know what size bolts are used to attach
the CNC mountings on Sherline Mills (the mounting cup that attaches
to the mill)? I have a metric mill, and though I bought both a 12key
metric and a 12key inch set, none of them actually fit. :/

Before I go out and buy a 24/36 key set, it'd be good if I knew the
size. :)