These brackets are designed to replace the original rear mounting point on the SW20 side vents.
The original metal strap is often rusted and breaks when removing these panels. 
Likewise the fiberglass mounting posts often crack and break off. 
This replacement bracket locates over the original studs to ensure correct positioning. Once glued to the side vent it gives a much more robust fixing point. 
The kit comes with brackets for both the left and right side along with new stainless steel bolts 
I recommend an epoxy such as Araldite or JBWeld for a strong fixing but any good adhesive should be suitable as long as the area is cleaned and properly prepped before fitting.