Both the Landing Pad 6 and 7 and are used for custom applications. The difference is the type of mounting hardware each has.
Landing Pad 6 is used in caps, or other applications where you can gain access to the bottom of the roof, these use a "cap nut".
Landing Pad 7 is used on sheet metal applications such as the roof of a car where you you cannot easily access the bottom of the roof. These use a "Blind" fastener and should only be used in sheet metal.