First choice would be Throw the thing in the scrap bin where it belongs and start again.!!. . . OR. . . Failing that A simple fix would be use a thrust bearings at coupler side of profile, presuming the other has deep grove bearing, and thread the shaft and put locking nut on.

Better way would be machine the profile to accept angular contact bearings then thread the shaft and lock nut or use Bearing block machine screw to fit.!

First choice would be best solution.!!. . . . . . If you wan't to know all the hassle coming your way with if you continue with this pile of shite then just contact Micheal (M.Marino) has he's been there and pay'd the price. Honestly not worth the price of the thrust bearings in my experience.!!