So I sourced the optional C-10 Concours backrest and carrier rack pictured and it clamps to the hand hold with two brackets which I have. Does anyone know the bolt sizes that are used ? Also, there are support brackets on either side of the carrier itself....and it looks like one bolt goes down from the top of the bracket.....while the other bolt goes up through the side bracket and into the clamp. Is this correct ? Are these two bolts the same size ? Any advice is appreciated !