The Teletype Model 40 also used a spinning belt that held type slugs (IIRC, the same ones that the Model 28 used back in the 1950's). Only it was a rubber belt

The Teletype Model 40 also used a spinning belt that held type slugs (IIRC, the same ones that the Model 28 used back in the 1950's). Only it was a rubber belt not a metal chain, so it didn't require hearing protection to run with the covers open. ;) Based on the text content of the line you were printing, the sound would change from a "brap" (not many duplicate letters on the line) to a "braaaaaaaaaap" when you had lots of the same character, like when someone used the equal-sign as a section separator between paragraphs. One location on the belt held a metal flag not a type element, and that was how the electronics knew the start of the type element sequence. One of the fun pranks you could do was to swap a couple of the type elements...