Works great on pinnacle 34mm tube scopes - SightMark Bubble Level Rifle Scope Ring

Not the world's most beautiful bubble level, but it gets the job done, is very light, and isn't a pain in the royal behind to install level to the scope itself. It's a little "clunky" looking on the left but the benefit of this design is you can install it without having to remove an already-installed scope since it splits in half.