I had a Bartech for 6 years...A few months ago, I rented someone else's bartech and he had these rings. Wow. I never knew about them. They're so much better than the plastic rings or worse...the strips...I wish I knew about them before.
Aluminium Focus Ring
Durable Aluminium Focus Ring for the BarTech Handset (BFD).
These rings are great. They eliminate a lot of fumbling around with the flexible tapes when changing lenses. And they mount in an accurate way that allows for semi-permanent distance marking when using a known set of lenses.