Align the /dev/mount to the 19” rail with the threads facing you. Guide the /dev/mount in from behind the rail. The threads should align with the top and bottom hole of the rack unit, the hook going through the middle hole. The hook must lock with the rail.
Make sure to hold the /dev/mount straight. Push the tip slightly towards you and while doing so use your thumb to push the front end of the clip from the side towards the 19” rail until it snaps in place.
Now take the hardware (with 15kg or less) you want to install and place it on the threads of the /dev/mount.
Take the hex nuts and fasten them by hand. Only by hand. Do not use tools to tighten the hex nuts! Maximum torque of 3Nm – more can deform your 19“ rail and/or your equipment.