Current Designs (CD) kayaks with retractable skegs all come with this style of skeg knob.

The main reason to replace control knob is because you needed to straighten or replace a bent skeg cable and the knob broke when you tightened the set screw.

To replace the knob: loosen the set screw, pull the skeg blade down and/or unhook it from the pivot such that only about an inch of skeg cable is sticking out the control recess near the cockpit, push the stainless steel stiffener tube aft until the front edge of it clears the front of the controller recess, then tilt the stainless steel stiffener tube so you can pull it out of the boat and replace the skeg knob.

When reassembling, adjust the skeg blade so that the lowest corner projects about 3.5" from the bottom of the hull. Make sure the skeg cable is inside a stiffener tube, be sure the knob's setscrew is lined up with the hole in the Stiffener Tube, if you miss this hole you may break the knob. When the set screw hits the steel skeg cable it should feel solid and not make much noise. Don't over tighten the set screw. Tighten it just enough that you can move the skeg blade without the cable slipping in the stiffener tube and the tighten the set screw about 1/8 of a turn more.