[DonRotolo]

This could be done with a 1/4" axle at the center pivot, and a 1/2" axle in the same spot could fail. It all depends.

A big factor is the unsupported length. If you keep the length between supports to a minimum, say 1.5", and that weight on the end is under 20 pounds, you'll be fine with 3/8". That is, the axle can be as long as you need, but the 'business part' should be as short as you can make it without the long arm being too weak. PM me if that's not clear, i'm having a hard time tonight...