Lug (bicycle part)

Lugged steel frame construction is a method of building bicycle frames using steel tubing mated with socket-like sleeves, called lugs. For most of the bicycle's history, steel has been the primary material for bicycle frames, with lugged construction the primary assembling method. Steel continues in use by builders of high-quality steel frames, though its dominance as a frame material has waned since the mid-1990s – displaced largely by aluminum and TIG welding.