Parts that say "Schwinn Approved" were made elsewhere to Schwinn's specifications. The parts that say "Schwinn" were made by Schwinn in their enormous Chicago factory (which I had the pleasure of touring in the early '70's). These rims, like the Chicago frames, were among the sturdiest ever built. They also manufactured their own rims in the Chicago factory, the "Schwinn Tubular Rim". Older Schwinn " cruisers", such as the Excelsior that was the inspiration of the first mountain bikes, used a straight lower top tube from the bottom of the head tube to the seat tube. If I recall, it was what Schwinn called a " cantilever" frame, where the seat stays pass by the seat cluster and continue on in a graceful curve to join the bottom of the head tube. The Typhoon probably dates from the late '50's or '60's. NEW! Mike Rother has an excellent overview of the fillet-brazed lightweights, also on this site. Muller has a very detailed explanation of this process, in his superb article: Inside the Varsity, which is now on this site. There are necked-down parts that fit into the top tube and down tube, like internal lugs. The head tube and the tapered segments that lead into the the top tube and down tube were actually made from two special forgings that were "electro-forged" (welded) together down the centerline, then ground smooth, so the seam is not usually visible. The head tubes look as if they were fillet brazed, but they weren't. With the exception of the Sports Tourer, Super Sport, and Superior, they are welded, not brazed. The Chicago Schwinns were among the most bomb-resistant bikes ever built, and they were built with unique technology.