Standard： DIN 6923. Thread Size：M3,M4,M5,M6,M8,M10,M12,M14,M16,M20. Flanged nuts with serrated face. M8： thread pitch 1.25mm， spanner size 13mm. M4： thread pitch 0.7mm， spanner size 7mm. M20： thread pitch 2.5mm， spanner size 30mm.
eBay