6mm M6 A2 STAINLESS STEEL COACH BOLTS CUP SQUARE CARRIAGE BOLT SCREWS - DIN 603
These are a DIN 603. Further details are as follows M6 CARRIAGE BOLTS - A2 STAINLESS STEEL. BA Screws, Nuts. BSW Screws, Nuts. UNC Screws, Nuts. Thread Pitch - 1.0mm. Square Section (Under Head) Depth - 4.6mm.