These mirrors have a very sturdy construction with the thick rubber edge protection. The single centered swivel mount is the "BROSSARD" heavy-duty mount so double swivels are not needed on the larger sizes.
(NOTE: We have seen many descriptions of mirrors on the Internet stating that they have a heavy-duty mount. The "Brossard" swivel is the only heavy -duty swivel mount we know of. Heavy Duty mounts are galvanized steel and not painted.)