The plastic roller bath assembly is also known as the roller waste collector. This unit is disposable and does not have a replaceable knife. This item is backwards compatible and may be used in place of the metal roller waste collectors used on all polyjet desktop printers. Stratasys no longer supplies replacement roller knives, so rebuilding the metal roller waste collectors is no longer an option. This item is covered under a Diamond Care service contract, but we recommend customers keep a spare for their printer. Grease has been pre-applied to the roller knife in order to reduce friction against the roller. Care should be taken when handling so the grease is not disturbed and the knife is not dented or damaged.