I spent many hours in the bomb bay of a B-26 treating these for corrision. They are made of some steel alloy and exhibit rust. Manufactured by the Mallory Battery Company during WWII. As I recall, one arm is to release the bomb and the other is to set for arm or salvo.
Here are two images of these bomb release mechanisms. The one has a bomb shackle mounted so you can see how the release mechanism arms connect. And you see the word 'ARM', which if not engaged, then the bomb is salvoed.