The Stokkermill HM hammer mills are systems for reducing the size of incoming materials, in order to allow subsequent separation and cleaning operations with the aim of maximizing the commercial value of the output materials. Stokkermill designs and manufactures small and medium sized hammer mills that are characterized by their robustness and simplicity during maintenance operations thanks to the hydraulic opening system of the crushing and rotor lifting chamber or the replacement of the grading grid. The simple construction and the use of high quality materials guarantee the durability and reliability of the Stokkermill hammer mills. The hammer mills can be equipped with an inverter to optimize the rotation speed according to the material to be processed; a particular system for anchoring the crusher to the base allows vibration reduction. A safety system allows the automatic ejection of any foreign bodies, avoiding damage to the rotor and the crushing chamber.