Those are bottom covers for ZMR250 quadcopter frame, I made them from scratch in 123D design for my own use. They will serve as protections for escs that I will attach under main carbon frame.
Slim version has around 10mm space inside (from inside-bottom to top-edge), tall version have 13mm
Holes are for M3 screws with round hex heads (dont know proper term)
I've printed it upside down for best results, and I advise doing the same.
Based on Zmr250 carbon frame, designed in 123D design