Today I went to B+Q to get bolts to join my toilet cistern to the pan .I dropped one when taking it apart yesterday and it had vanished . They had coupling kits but as I only nedded the bolts I chose what was descibed on the packet as .Cistern Close Coupling Bolts " When I opened it at home it seemed from the instructions ( which seemed to cover push button/hinge and cistern coupling options and are pretty poor ) I saw that the bolts were what looked like M6 bolts with slotted pan-heads ,threaded all the way to the head and did not have the square section below the head as I expected . It might be that they will do but the diagram in the kit shows the way they should be fitted the but the screws in the diagram do have the square section so looks like I'll be going back to B+Q .. Might just root around in their nut and bolt section to get a couple of suitable bolts
Stuart