Hammer mills are aggressive pre-cleaners designed to remove appendages. They use “hammers” attached to a horizontal shaft that rotates inside a compartment with an interchangeable, perforated, outlet screen. Appendages, awns, and other chaff are removed as the hammers vigorously scrape the seed over and through the screen. Holes in the screen must be large enough to allow the seed to pass through without damage, but small enough to remove appendages. Screen with openings of various sizes and shapes are available. The shaft speed should be adjustable. Units are equipped with baggers for the processed seed.