This is where you select your nock and protector ring or your arrow. The Protector ring is only for the CT Cheetah 400 and 500. If you select "None" for your nock, you will receive the standard nock and style that comes with that shaft.
The standard for shafts are as follows:
 
CT Nock - CT Whitetail, CT Cheetah, CT Rhino and Safari, CT Panther and CT Lynx.
McKinney Nock and Nock Adaptor - CT Buffalo 27, CT Hippo, and CT McKinney II