BS 10 is British flanges standard, flange rating table D, table E, Table F, Table H and so on, flanges type ring plate, blank, screwed, backing ring for HDPE pipes. BS 10 flanges are all different to BS4504 flanges, they can't instead of each other, BS table D flanges are very thin, it is usually using for backing ring with hot dipped galvanizing for HDPE pipes connection.