Replacement cast steel ribbed spool for most disc harrows with 1" square axles and 7-7/16" blade spacing.  Listing is for one cast steel spool with four (4) ribs, overall length is 7-7/16" but most sellers list them as 7-1/2" overall length, with a square hole clearanced  for a 1" axle. These are designed to fit loosely on the axle to allow proper alignment of the disc blades These ribbed spools are lubricated with grease inside the bearing caps and should be greased before each use and every couple hours during use! This same ribbed spool can be used as the spacer spool between disc blades where a bearing is not present.