Assertion: siding's rail | /r/HasAspect | flat bottom
Facets:
Source sentences:
text: In the 1830s Robert L. 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.