Occassionally we get contacted about a new drag knob not fitting on a reel. Shown above is the newer style 52N-750N Power Drag Knob. It's an improved design with stronger plastic and a better internal drag spring system. Penn has made similar improvements to other drag knobs.
1) Spool not seated down on the shaft.
We see this problem even with older style knobs.
Spool is not seated all the way down on the shaft, making it impossible to screw the drag knob on correctly. FIX: Adjust the drags inside the spool so that they line up and the spool will drop down onto the shaft. Series of three photos:
The first image shows the spool not seating down all the way on the shaft. The second shows the edges of the drag washers inside the spool being slightly out of alignment. Use a flat edged screw driver to line them up, then you'll get the third image as a result: The spool seated properly on the shaft.
2) Part of the old knob is still on there.
The inside of the old drag knob is on the spool, commonly it's the nut and the spring. FIX: Remove these old parts, there should be nothing there but the spool, it's drags and the point of the shaft before you screw on the new drag knob.