I transferred the floor-to-lag- screw measurement to the other stud locations with a level.
The lag screw locations should be predrilled to a diameter just under the minor diameter of the lag screw threads. I use the largest drill bit that cannot be seen when lined up behind the screw threads.
I pre-positioned the box rail brackets at the lag screw loca- tions on the box rail.
Starting with the center bracket, I attached all of the box rail brackets to the wall with the lag screws that came in the kit.
A socket attachment on an impact driver works well for this job. I then rolled the wheels of the hangers into the open end of the box rail.