Indy produces Bimini rings in sizes  2inch and 2.5inch - you can place rubber inserts for smaller sized tubes.

These are 6061 Aluminium Polished - there is a standard size thread to take you bimini's thumb screws- also the bolts to attach the bimini ring are from the inside position - so viewing the ring from the outside of the boat you only see a nice polished ring.