In one aspect of the invention, a rotary shaft impactor has a rotor assembly connected to a rotary driving mechanism. The rotor assembly has a plurality of autogenous bed pockets, the pockets having a wall intermediate a distal and a proximal end. A least one of the pockets comprises a plurality of inserts arranged adjacent one another in a row and attached to at least the proximal or distal end wherein a first end of at least one insert is complementary to a second end of an adjacent insert.