I was lucky enough to photograph an original prop arm used in the movie Terminator. I've seen one before, from Terminator 2: Judgement Day, it was made out of metal and weighed quite a bit. This one though, was made out of some kind of resin with steal wire underneath for support. It was pretty fragile and probably weighed around a pound.
Prop arm from the movie Terminator
Prop arm from the movie Terminator
Prop arm from the movie Terminator