Had a problem with the shoulder hubs falling out as they were only held in by friction. Decided to JB Weld a piece of 1/4″ threaded rod to the back of each, I drilled a 1/4″ deep hole in the back center of each hub to help hold the threaded rod. Once the JB Weld dried, I inserted the hubs into the legs and used a strap strip of styrene (drilled a 1/4″ hole), a washer and a wing nut to hold it all in place. Definitely not going to fall out this time.
Cost: $x for 1/4″ threaded rod and wing nuts