Elsewhere T rails were replaced by bull head rails of a rounded 'I' or 'figure-8' appearance which still required a supporting chair. In North American practice the flanged T rail became the standard, later being used with tie-plates. Stevens invented the flanged 'tee' rail (actually a distorted I beam), which had a flat bottom and required no chair a similar design was the contemporary bridge rail (of inverted U section with a bottom flange and laid on longitudinal sleepers) these rails were initially nailed directly to the sleeper. By the 1820s the first shaped rolled rails had begun to be produced initially of a T shape which required a chair to hold them the rails were held in position by iron wedges (which sometimes caused the rail to break when forced in) and later by wooden wedges, which became the standard.
