Toff the feet are four inches wide and fit on each end of the box section.
The box section is made from 2inch x 1 inch 3mm aluminium.
If you were converting an aluminuium ladder, you take the standard feet off and shape some hard wood so that a 6 inch piece can be hammered up inside each end. You then cut and file the ends so that the box section can fit up inside.
The hardwood inserts prevent the ladder walls from crushing as you have to drill and put a bolt through each side and tighten them.
The tyre strips are 4 inches wide and have to be long enough to go round the channel section, leaving a gap at the bottom that will take a 2 inch diameter piece of industial heavy duty hose. This is important for the suspension system to work.
you bolt the rubber to the channel section[ 2 each end] using penny washers that wont pull through the rubber. You then insert the 2 inch diametre hose and fasten them with cable ties.
When you go up the ladder, you can feel the suspension, the rubber pushes back away from the ladder. The ladder then has to actually push this rubber foot in order to slip back and it can't. I hope all this makes sence. Dai