I was about to buy a Snap On jam nut tool for $60 when I came across a thread on H-T that had instructions on how to build one.

You will need the following:

10mm 3/8 drive deep wall socket
5/8" wrench
flat head screwdriver

All you have to do is hammer the 10mm socket into the 5/8" wrench and stick you screwdriver in the hole of the socket.

If you want the tool to be 1 piece, find a flat head screwdriver that has a tip wider than the hole in the 10mm socket and hammer it in. I had to grind a little bit off of the side of the screwdriver to make mine fit.

Here's the end result:










Thanks to UncleBen'sRacing for the instructions.