I build synth modules in Kosmo format, which is electrically (almost) the same as Eurorack but larger. Eurorack PCBs can be used to make Kosmo modules, but board mounted pots are usually too close together and jacks are too small, so need to be replaced with panel mounted parts. Some PCBs are meant to be mounted to the front panel using these board mounted parts, so in such a case a solution like this is needed to secure the PCB to the panel. The bottom piece fits between a pot and the panel. A pan head M4 or M5 machine screw holds the two parts together and clamps the PCB in between. (In the photo, I didn't have a pan head screw the right size, so I improvised with an additional nut on a flat head screw.)