Heavy-Duty Roller Guide-On System Heavy-Duty Roller Guide-On System provides a worthy assist while getting your boat on and off its trailer, helping you load and unload faster and safer. Attached to the trailer frame, the pair of guide-ons helps center the boat on the trailer, preventing wind and currents from derailing your loading attempts, while the uprights provide a sight line at deep launches and in murky waters. The rubber rollers provide a soft touch for your boat, while its steel construction withstands nearly anything you can throw at it.