the main orange part of each pad has always been made of aluminium.
underneath the rubber rim is a thin trigger hoop that in early production kits was made of aluminium, but due to breakages has long since been made of polycarbonate plastic. if the pad has 5 o-rings there is no chance that the trigger hoop will be aluminium. note that you cannot see the trigger hoop without removing all the lugs and dismantling a pad.