Its basically just a socket one end that fits the stump of his forearm, and a clamp on the other end. Mike still has a few inches of his forearm. I met Mike back in 2003. Really nice guy, and crazy strong.
I have a guy who lives near me that comes to work out occasionally, he has the same prosthetic arm, but also lost his leg, so he has a prosthetic leg as well.
Guys like that who have a disability, and not only persevere, but still kick ass are some of the coolest athletes out there. It really shows true inner strength, and pretty much shoots down any excuse anybody on the planet can come up with.