I bought the Falcon CP130 frame and the Spedix IS100 20A Mini-Tower. The M2 4mm stand-offs that came with the mini-tower was killing me. The threaded part broke off easily and the base was 1 mm too much that prevent each board in the tower from full seating their pins onto the next board. Thus, not leaving any room on top of the stack to fit an FrSky R-XSR.
So, after tearing the cheap Lipo strap that came with the frame, I decided to take everything apart, design my own hollowed out spacers 4mm tall, so that I can use a single M2 screw 21mm length for all four corners, and print it out using TPU filament at 100 percent in-fill.
Once I screw in the nuts, the spacers can compress just enough to get all the board pins fully seated, and thus, have room on top of the stack to fit my radio receiver. Going to re-do my FlyEgg 130 to use these spacers as well.
Tip: If you want to use this spacer for the bottom of your PDB/ESC board, I just chop off the X part and use the four corners as stand-offs so that the X cross support doesn't get in the way of the Lipo strap. Works well.