This assembly comes with 2 screws and 2 spring loaded nuts like these https://www.dold-mechatronik.de/selectable-sliding-block-with-spring-B-type-groove-8-thread-diameter and that allows you with M5 screws to secure the camera mount into the rail of the central aluminum pole.
This is the kit - https://www.dold-mechatronik.de/Reprostativ-V5-kit