I made myself one from a piece of 5/16" by 24" long hex stock that I cut to 16" length. Had to order it from Grainger Supply. Worked very well for me. You might be able to make one using a long piece of 1/4" square (key way) stock (available at the big orange lumber place), a 1/4" drive 5/16" hex socket and a length of 5/16" allen wrench/hex key cut off the long end if you can't wait for the hex stock. You would have to tape the pieces together so they don't come apart and end up at the bottom. I do know that my 3/8" drive long extension with a 5/16" hex socket would not fit through the intermediate shaft bushing.
