A rotatable cutting drum comprising knife holders for attaching cutter knives thereto. Each knife holder comprises a forward member and a rear member and a knife connecting portion. The rear member extends from the connecting portion towards the rotational axis of the drum and has an extension member which extends circumferentially of the rotational axis in a direction opposite to the direction of rotation of the drum. The forward member extends from the connecting portion towards the drum rotation axis and abutts with the extension member of an adjacent knife holder positioned forward of the knife holder in the direction of rotation of the drum.
