M3 x 0.5mm SERRATED FLANGE NUTS A2 STAINLESS STEEL FLANGED HEXAGON NUT DIN 6923
These are a DIN 6923. Further details are as follows M3 M4 M5 M6 M8 M10 M12 SERRATED FLANGE NUTS - A2 STAINLESS STEEL. BA Screws, Nuts. BSW Screws, Nuts. UNC Screws, Nuts. Across The Flats (A/F) - 5mm.