Abstract: In a hammer breaker for breaking and crushing scrap material, particularly scrap metal, in which a hammer rotor having a plurality of hammers pivotally mounted thereon is rotatably mounted about a horizontal axis in a housing having an inlet for the material to be broken and crushed, and an outlet for broken and crushed material at the top of a shaft which is located above the hammer rotor and is arranged to receive material tangentially from the rotor, the outlet being covered by a classifying grate which extends across the top of the shaft, the grate is mounted adjustably, preferably pivotably, relative to the shaft. This enables the effective size of the grate openings through which the broken and crushed material can escape to be adjusted according to the size and density of the scrap lumps required without having to change the grate.