Grinding Balls Rods Mineral Processing Metallurgy. · Grinding Balls. Steel balls ranging from ¾ to 5 in. in diameter are used. Rods range from 1½ to 4 in. in diameter and should be 3 to 4 in. shorter . Grind ball ball mill – RexLine. Technical Specifiion: We make the grinding media in various specifiions.