Rugged Nicholson Knife Arms Nicholson Knife Arms are self-opening for safe, simple and reliable operation and for increased log end protection. The end of the incoming log opens the knife arms. The log meets the opening edge of the arms and smoothly spirals the arms open. This is important in making sure that even the very first few inches of bark are removed from the log. Both Nicholson Air Seal and Air Cell Rings use the same knife arms. All Nicholson Arms are made of high alloy steel for superior strength without sacrificing reparability. Bent arms can be both welded and straightened. Three types are arms are available: Nicholson T-Section or ‘Standard’ Arms have replaceable knife holders and are used in most applications. Nicholson Two Piece Plate Arms consist of a flat plate and separate hub. When servicing these arms the heavy hub section can be left on the ring, making it easier to transport the arm. These arms are used often in higher speed applications and for frozen wood. Patented Nicholson Stringy Bark Slitter Ring Arms are also available to debark problem species like Redwood, Cedar and Eucalypt. These arms are used in Nicholson tandem ring debarkers with a second standard ring to cleanup the short bark segments created by the Slitter’s disc type cutter. Slitter Arms are generally opened by a timing process and not by self-opening.