Boat trailers often feature an insufficient number of rollers, ones that do not touch the boat or even no rollers at all. Many boat manufacturers recommend better support for the keel and transom as a way to further protect your investment. Adding a few of our keel rollers to a bunk trailer greatly reduces the effort needed to launch and retrieve your boat. It also shifts some of the weight from the carpeted bunk to the roller, providing a buffer between boat and trailer. Our rollers: Improve support for the keel and transom during transport, Allow for easier boat launching and retrieval, Eliminate the need to submerge the trailer to float off the boat, Keep the tow vehicle safely off the slippery portion of the ramp, and Reduce damaging friction between boat and trailer. Old Part Number: RP-404.