Hammer mills with a tip speed of 13,000-18,000 fpm will produce a high quality finished product with excellent capacity and efficiency. 38" diameter mills with 1,800 RPM motors (17,800 fpm) and 44" mills with 1,200 or 1,500 RPM motors (13,500 or 17,250 fpm) are both used extensively in the processing of all kinds of feed ingredients.