Dutton-Lainson's 4-foot roller bunks (pair) attach directly to 2 x 4 bunk boards, or can be mounted with 6389 brackets (sold separately). A quick, easy and inexpensive way to upgrade bunk trailers to rollers. Features 12 gauge steel, galvanized finish and rubber rollers. For boats weighing up to 2,500 lbs. The advantage of this style of roller bunks is that each set of rollers is wider (3 rollers instead of 2), providing more contact with the boat. The rollers on this style of bunk do not have wobble capability for self-alignment like model 6354 does. The rated capacity is based on having good contact with all of the rollers, and a reasonably even distribution of weight on the rollers. Rollers must be in contact with straight sections of the boat hull. It is critical to avoid a very large load on the first set of rollers during the unloading and loading process. The boat should float at least part way onto the trailer before contacting rollers, so that all of its weight is not concentrated on the first set of rollers. A concentrated load can crush a single set of rollers, with the potential for damage to the boat hull.