I did call Skidim.com and they were awesome to work with. The reason I was asking what size Hugh was told to use was I originally saw where a guy used 2 wraps of 5/16 flax style packing so that is what I got. When I put 2 wraps in, it filled the packing nut nearly all the way to the end barely leaving enough thread to get it started before starting to cinch up and compress it ( by hand ). i had to put a wrench on it to tighten it down far enough to expose the hole in the rudder so the cotter pin would go through, but felt like that was tighter than it should be? It took all the slop out of the rudder and it turned fairly freely, but as the Washington summer has ended, the boat is not in the water, the fuel tank is out, so I really couldn't test it. ( I did have the rudder wedged all the way up blocked in that position to help expose the holes and make sure the rudder was in the correct position).
After calling Skidim, they recommended 1/4" packing so I repacked it with 1/4" ( the new style not the flax packing). After putting in the 2 wraps of 1/4" I could see where it did not fill the packing nut out as far making it easier threaded down far enough to get the cotter pin in without "reefing" on the packing nut, but when looking at it before I screwed it on, there was a little clearance between the diameter of the hole in the nut and how far the packing filled it out ( not compressed ?).
It actually looks like the 5/16 was a better shaft diameter fit, but the 1/4" fit the gland nut better?
There was virtually no slop with the 5/16, and unlike a drive shaft, I don't see heat being any issue from friction. The 1/4" packing allows for just a little rudder slop ( 1/16 -1/8 maybe grabbing the rudder from outside the boat).
I'm curious if the 5/16 would have swelled up and got tighter as the whole reason for repacking it was the steering was way to stiff while on a plane. The 1/4" was not flax and indicates that it does not swell and shrink like flax packing so I am hoping this is the right answer to the steering problem. Unfortunately it will be next may before it hits the water again to try it out.