The surface pits are a result of sand casting when the molten material is poured into a preparation shell form made from sand and binders. At times air pockets can occur and also piping is the small hole often seen at the ends of the magnet as it is formed. Magnet rods and bars are often molded oversize and rough shaped in a particular cast. The rod magnets are center-less ground to the desired OD (outside diameter) and cut to the desired lengths. During this process, chipping can occur on the ends of the magnets during the chamfer (angle) process. Fine Aluminum Oxide or Diamond wheels are good for grinding Alnico magnets.