1. In an impact crusher, a combination comprising a housing having an inlet for material to be comminuted and an outlet for comminuted material; a rotor provided with beaters and mounted in said housing; an impact or grinding means mounted in said housing for movement toward and away from said rotor and defining therewith a gap through which the material to be comminuted passes on its way from said inlet toward said outlet and is comminuted by said rotor beaters and said impact or grinding means; and adjusting means for varying the width of said gap, having a lost motion to allow the impact or grinding means to yield in direction away from said rotor and including carrier means connected with said impact or grinding means and extending from said housing, holder means connected with said carrier means outside of said housing, motor means operable to move said holder means at least in a direction to increase the width of said gap, and at least one insert mounted at the other side of said housing and having portions of different thicknesses, said insert being movable between said holder means and said housing to thereby determine the minimum width of said gap depending on the thickness of that portion of said insert which is located between said housing and said holder means.