And I took a couple of pictures with the castor assembly quickly mounted to the main axle, note that when it is actually mounted, it will be shorter, I just cut it at that length to give me room to work.
And finally, one close up of the tee. The tee is 1/2 inch, and the bushings and nipples on the main axle are 3/8, that size chosen because the ID of the nipples fits the main axle's OD almost perfectly. As mentioned previously, the 1/2" nipple was reamed out to let the castor assembly's rod to fit into it nicely. When completed, the 1/2" nipple and rod will be match drilled and bolted together to prevent rotation, and the nipple itself will be tightened into the tee, match drilled and bolted, also to prevent rotation.