This is a 2 part print :

The inserts fitting inside the rails and then the mount that attach to the inserts. This design allows to mount an external peripheral on the Sovol frame without drilling any holes. you will need M3 screws for the fixing. 

All the holes are threaded for M3 screws

The inserts are secured by inserting a M3 screw which will exert pressure on the outstide of the insert and tighten against the rail.