My Handi takes a 1/4 by 20 set screw- get the shortest available.
Remove the forearm screw and forearm.
Insert the set screw into the forearm screw socket.
screw it to the bottom just "finger tight".
re- install the forearm and screw the forearm screw
Check for forearm clearance, if still too tight, remove forearm screw, and back out set screw and repeat until the forearm has the desired clearance.
If there is not enough threads available for a good connection the forearm may still need some filing/sanding to gain extra clearance.
Back out the set screw noting the number of turns required to release. Apply Locktite and re-insert the set screw the required turns, let the Locktite set then return the forearm and tighten the forearm screw. I also apply a small amount of grease to the tip of the forearm screw to help reduce the friction between the set screw and forearm screw.
Anyhow that is the way I did it