Visitors: 3680. CAD/BIM Library of blocks Stairs concrete stairs. Free CAD+BIM Blocks, Models, Symbols and Details. Free CAD and BIM blocks library - content for AutoCAD, AutoCAD LT, Revit, Inventor and other 2D and 3D CAD applications by Autodesk. CAD blocks and files can be downloaded in the formats DWG, RFA, IPT, F3D.