Here's an internal view of the Bendix Junior.
There were a bunch of different hub configurations from 12" to 16" to 20" that I remember. From the 24 hole .105" drilled hub that used conventional spokes and rims, to well into the early 1980's using the 16" and 20" Skyway Tuff wheel. There may have been more? There were a lot of juniors used inside weld spoke wheels. By weld spoke, I mean the wheels had the spokes spot welded to the rim. Some weld spoke wheels had pneumatic tires using a conventional tire and tube. Others had a semi-pneumatic or what was called a solid tire. Could do a page or two on how to install solid tires on a bicycle wheel LOL. Wondering if you could even find some good solid tires today that are not petrified by age? Later on, the Skyway or Sun composite wheel, that I remember, took over the juvenile market and I remember seeing the last of the Bendix made brakes, mostly the junior model, used on those type wheels. Shimano and NK took over the juvenile coaster and most of all the coaster market from that point on. Don't know what they use now? Thanks!!!