Abstract: A slim knife unit includes a guide member having an L-shaped body which supports an elongated fluid actuator comprising a piston connected by piston rods to a base member having a sliding track connection to a removable knife holder. The knife holder has spaced walls defining a slot which receives a circular knife supported by a bearing mounted on a spacer bushing clamped between the walls by a center support screw. The guide member has a linear track which cooperates with the rods to guide the knife holder, and a releasable latch secures the knife holder to the base member. The guide member also has a linear track which guides a clamp member movable by a screw for securing the knife unit to a support bar.