Used to hang light fixtures between joists or structural members (not designed for ceiling fans). Expands from 14-1/4" to 22-1/2". Can be used on 16" or 24" centers. Furnished with 3/8" -18 NPS fixture stud. Box mounts to bar through center 1/2" box knockout and is adjustable alongs the entire length of the bar. Has knocking tabs for secure installation. Box must be ordered separately. UL listed.