Different Types of Pocket Knives

traditional pocket knives (slip joint) - When we say traditional, we are referring to the original slip joint pocket knife.  This is a general pocket knife for general use.  Most of your Case XX pocket knives are slip joints, for an example.  They fold open and close, but at no point are they locked.  There is a spring device between the liner of the knife that holds the blade open or close.  It only takes pressure on the back of the knife blade to close it.

lock backs - A lock back pocket knife is an advancement of the traditional pocket knife.  It also has a spring device to hold the blade open.  However, the spring of a lock back has a hook made in it, and the blade has a notch in it.  When fully opened the hook and notch line up, which in turn locks the blade in place.  The blade will then stay locked until the operator presses on an exposed part of the spring, located on the back of the knife.  When you press this exposed part of the spring, it disengages the hook and notch.  You can then fold the blade back into the handle.  This makes a lock back knife safer than a traditional pocket knife, because the blade cannot close by accident.

liner locks - The liner lock has a leaf cut out of the liner that acts as a spring.  When the blade is fully opened, this leaf springs over in front of the bottom of the blade, locking it in place.  So it is actually the liner of the knife that is holding it open.  Hence the name, liner lock.  To close the knife, you push this leaf of the liner over, usually with your thumb, while pushing on the back of the blade.  The liner is then out of the way, allowing the blade to fold back into the handle.  These knives are also safe from accidental closings.  Liner locks are also popular for one hand opening and closing.

frame lock - Frame locks are very similar to liner locks.  However, instead of part of the liner acting as a spring and locking the blade open, it is a part of the frame of the knife.

assisted openers - Assisted opening pocket knives use a type of technology that springs the blade open once started by the operator.  Different knife brands have their own systems, such as Ken Onions SpeedSafe technology for Kershaw, or F.A.S.T. (forward action spring technology) technology developed by Butch Vallotton for Gerber.  These knives are usually liner locking knives.  People have compared them to a switchblade, but you do not push a button to open the knife.  Nor does the blade come out of the end of the handle, but instead the side of the handle like other pocket knives.  Many of them have thumb studs on the side of the blade.  Once you start to open the blade by pushing on the thumb stud, the technology assists the opening by springing the blade forward.  Hence the name, assisted opening knife.  These are also great for one hand operation.