Adjustable bar hanger -Maximum load 17Kg/50LB -is the load for vertical or horizontal position?
You typically put this horizontally between joists or trusts so you can center an electrical box.  The 50LB load will be pulling down on the bar hanger.  

To support an octagonal box between trusts.
Adjustable from 11.5" to 18.5"
Maximum load: 50 Lb (22.70 Kg)
Not intended for ceiling fan