I asked the mfg. and below is the answer , I received back
Q: What is the difference between the ratchet and nape strap suspension liners?
A: Both suspensions are fully adjustable and are positioned at the nape of your neck. The nape strap adjusts by a Velcro strip usually referred to as a one time adjustment. The ratchet adjusts by an adjustment knob allowing for quicker adjustment in the field.
Answered on 5/24/2012 by Butch