Extreme Max 3005.3822 Heavy-Duty Roller Guide-On System Includes one pair of Heavy-Duty Roller Guide-Ons with an easy, bolt-on installation that fits bunk or roller-style trailer frames up to 3" wide x 4.25" tall* Custom-formed 97 arms and 13" roller assembly; up to 14" (3" trailer frame) or 16" (2" trailer frame) of horizontal adjustment Zinc-coated for freshwater corrosion-resistance, not intended for use in saltwater or brackish water The size and shape of trailer frames can vary drastically, please measure your boat on the trailer before ordering to ensure a proper fit * 6" bolt kits are available for trailer frames up to 5" tall, see Extreme Max 3005.4065