While the steel frame skyscraper dramatically changed the skylines of cities like New York and Chicago with forms achievable only with the new technology of steel frames, the technology of assembling and filling the frames remained comparatively archaic. Riveting required teams of three to four men--a forgeman, a riveter, and one or two helpers. Rivets were heated in a forge to a red heat. The hot rivet was tossed by the forgeman or his helper to the riveter or his helper and placed in a hole. The helper then placed a dolly on the head of the rivet while the riveter manually hammered a second head on the narrow end of the rivet. By the late 1920s that process had become automated to some extent. The manual hammering of rivets was ultimately replaced after the introduction of pneumatic riveting hammers.