A while ago, there was discussion about Thundercracker being an awful toy, but it all centered around the fact that he had this huge left arm. I brought up the idea of attaching an arm from another toy, but that I didn't want to have to buy a new TC just for the arm. I jokingly said "So, yeah, anyone who wants to donate to the cause, let me know."
Clay was kind enough to do just that. Basically, Clay sent me an entire Cybertron Thundercracker, and I was able to take the right arm off one and put it on the left of the other.
While I've seen it done before, I've also seen that a few people didn't redo the new hand into a lefty. So I shaved down the old thumb and cut a groove on the 'back' part of the old hand to make the new inner palm. I puttied on a new thumb and filled in the old groove on the other side. Then I painted both hands black. They actually look better that way.
It's not the most professional job, but it's better than having a thumb on the back of your hand.
The arm sticks out the back in jet mode, but it doesn't look all too bad. (There've been worse -- take BW Dinobot's robot legs in beast mode, for example.)