Hexagon Head Hex Head Screws Bolts, ISO 4017. ● Standard: GB /T 5783 ( ISO 4017 ) ( DIN 933 ). M3, M4, M5, M6, M8, M10, M12, M14, M16, M18 Coarse Thread Fully Threaded. - M18 series is suitable for 27mm wrenches.
eBay