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Lugged steel frame construction

Prugnat type 62 D lugs.
Clockwise from top left: seat lug, upper head lug, lower head lug.
This seat lug joins the seat tube, top tube, and seat stays of a steel touring bicycle frame. It also has an opening in which to insert the seat post, and a clamp to hold the seat post securely in place.
Simple, pointed head lugs on this bike boom road bicycle
Elaborate hand-cut and filed head lugs which have been outlined in a contrasting colour (luglining) on a Hetchins frame

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 carbon fiber; lugging has been displaced by TIG welding.

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