cav,those screws also do more than just the scuff plates..

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ok cav,ive just done a tour of the yard here and what i have discovered is..hq has a smaller head and is a normal self tapper..hz depending on build plant it looks like has a larger head and 1 is a normal self tapper and one has the self drilling shaft similar to your picture..
wb statesmans ive looked at have the same screws that are in the ebay add with the larger head and self drilling shaft which will be why its a 92 prefix number..
i have not looked hard yet at hj or hx..i have taken some pics and will take a few more and do them all at once..