As shipped, it can only be used with the supplied clip, which is of poor quality.
I ordered Gator clips which are great, but I can't install them for now since the adaptor is glued into the bottom of the factory clip and the thread is something like an M5.
It looks to be possible to buy a K&M screw that will make 3/8" mounting possible (and in fact the metal part of this device is made to install those screws), but who knows when I need to order enough stuff again to avoid shipping costs for a 1.5 EUR screw to try that.
This is the screw I'll try in the future: <a class="article link" href="https://www.thomann.de/hu/km_raendelschraube.htm">K&M 3/8" Screw</a>