[Jamo]

I don't care what jack you use or what material it is made of--the center pad (wood, etc) is what should be holding the weight if it is to a flat surface. The gaps between fingers are to allow you to jack to a channel jack point to keep it from sliding. Obviously, folks using steel jacks wrong and having the fingers carry the load might not have a failure because of the strength of the metal--but arruminum dictates you use it correctly. The rubber pad is really there to keep the wood from sliding around just like the fingers are. Wood is the best medium for the pad IMHO.