@TURBO200R4 I want the broader head as well. The non-flanged bolt in the picture has a 14mm head diameter and is the size the flanged head would be after grinding down. I want the wider head that is 17.8 to 18mm wide. No one makes that head size standard except in that flanged style so that will be the route I take in the near-term.
This is an issue with commercial door hardware as well, screws and bolts sometimes have head sizes that are used nowhere else that I know of. Hinge screws have oversized heads that you can't find anywhere else.
Sweet! And they offer it in a black finish, which will match the black backrest. The head doesn’t taper at the edges of the head like the OEM, but it an extra 2mm wider than most bolts I am finding and stainless in black. Winner! (With ~$30 in shipping for the $5 order, such is life).