-
looks like this.
That's not M6
I need button head
It's not a button head either.
Check with your thread gauge, my screen ruler is pointing to that be M8×1.0, not the standard ISO coarse thread pitch M8×1.25. That will just make your quest even more challenging. If it were me, I'd bin the Hope clamp which is an ugly lump and get a cheap generic one with a pivoting nut which uses a common type of screw.
Thank you tester and @freezing77 @mespilus @cagimaha
Its for the Hope seatclamp looks like this.