It is a screwdriver in the arm with a technic pin and round 1x1 attach to the screwdriver. It holds decently, but still has tendency to fall out if you move it too much. I decided to make it not entirely purist and wrap a bit of paper around the tip of the screwdriver to give it little more grip.
Been lurking a while and finally gave in and ordered some parts. With all the Official Justice League members coming out, I decided to expand it a bit. Borrowed some ideas from what I've seen on here. Green Lantern Hawk Girl Cyborg Green Arrow Black Canary Atom Metamorpho Vigilante Plastic Man Justice League