If you look real close, on the strap I have running for a back s.bag support, is the helmet lock. I ordered the 1" one on ebay that purports it to be for a Harley, because it comes apart so the front part with the lock can be attached to anything flat just by drilling 2 holes. Not necessary to be on a 1" tube, although it could, but would stick out farther.
Brogue Motorcycles makes an awesome, simple helmet lock for under $30. It uses existing bolts under your seat, super simple and quick to install and use. You can check out photos of mine on Instagram @wtfastalfa