Putting it all together. I welded flanges to the top and bottom of the seat post sleeve. The spherical joint is slid between these pieces. Holes have drilled in the flanges for the hitch pin to be inserted. Note the use of a nut to lock down the spherical joint bolt to the top tub. Hint: loosen this nut when installing the trailer to the tow bike. Then, when in position, tighten the nut.