mag drills aren't the best on durbar Dylan, (which is what I assume you are talking about - chequer plate (diamond pattern) is much harder to find these days and generally in thicker plates), ... how thick is it on the flat? ... might be just as easy, as has been said, to just drill the hole and countersink by hand with each bit in a different drill -- depending on the plate thickness of course
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steel durbar and ali 5 bar tread plate..
can't even find a pic of the diamond pattern steel tread plate
not a lot of good with the plate flat on concrete