Rollers are an assembly of three major components: axle, tube, and bearings.  The length of a roller is defined in terms of the "between frame width" or "BF".  This "BF" dimension allows 1/16" clearance between the extension on the bearing and the side frame.  Remember, Indoff, Inc can build your rollers to nearly any "BF" dimension, so you are not limited in your product selection.  Frame thickness is also important information to insure proper assembly (with pin retained and regreasable rollers). Indoff, Inc rollers can be provided with special coatings like urethane and zinc plating upon request. To begin quoting a roller, we will need to know the following information; between frame dimension, axle size, tube size, and any sprocket or groove dimensions.