section_path: Parts/Blade/Folding blade features/Common locking mechanisms
section_name: Common locking mechanisms
paragraph_text: Common locking mechanisms
  
  In the lock back, as in many folding knives, a stop pin acting on the top (or behind) the blade prevents it from rotating clockwise. A hook on the tang of the blade engages with a hook on the rocker bar which prevents the blade from rotating counter-clockwise. The rocker bar is held in position by a torsion bar. To release the knife the rocker bar is pushed downwards as indicated and pivots around the rocker pin, lifting the hook and freeing the blade.
  
  When negative pressure (pushing down on the spine) is applied to the blade all the stress is transferred from the hook on the blade's tang to the hook on the rocker bar and thence to the small rocker pin. Excessive stress can shear one or both of these hooks rendering the knife effectively useless. Knife company Cold Steel uses a variant of the lock back called the Tri-Ad Lock which introduces a pin in front of the rocker bar to relieve stress on the rocker pin, has an elongated hole around the rocker pin to allow the mechanism to wear over time without losing strength and angles the hooks so that the faces no longer meet vertically.
  
  The bolt in the bolt lock is a rectangle of metal that is constrained to slide only back and forward. When the knife is open a spring biases the bolt to the forward position where it rests above the tang of the blade preventing the blade from closing. Small knobs extend through the handle of the knife on both sides allowing the user to slide the bolt backward freeing the knife to close. The Axis Lock used by knife maker Benchmade is functionally identical to the bolt lock except that it uses a cylinder rather than a rectangle to trap the blade. The Arc Lock by knife maker SOG is similar to the Axis Lock except the cylinder follows a curved path rather than a straight path.
  
  In the liner lock, an L-shaped split in the liner allows part of the liner to move sideways from its resting position against the handle to the centre of the knife where it rests against the flat end of the tang. To disengage, this leaf spring is pushed so it again rests flush against the handle allowing the knife to rotate. A frame lock is functionally identical but instead of using a thin liner inside the handle material uses a thicker piece of metal as the handle and the same split in it allows a section of the frame to press against the tang.