The R-3028 RC is a roll bar or bumper mount. The Machined Aluminum Bases attach to any round tube 1.5" to 2" in diameter and the rubber grips hold tools 1" to 2.5" in diameter (shovels, rakes etc). The R-3018 R uses the same rubber tool grips that hold 1" to 2.5" tools but the Mount fits on 3/4" tube.