Vintage Windmill and Wind Generator Forum

From what I can tell on the 1898 and 1899 model you could also get them with the Bell Hub instead of the V Arm Hub that came out in 1898. Probably not that common. I'm guessing the reason being you could update your Bell Hub frame but keep your existing Bell Hub wheel that had the hairpin flat iron arms and 31 inch sails.

You are correct, you could a bell hub on the newer frames. I had an r/a last year that had a bell hub on it. Same way as the 602 style hub on a 702 was available into the the mid to late 40's.

Also in 1907 Aermoter introduced the HEAVY DUTY R.A. model in 10 and 14 ft. Probably not common either.