TY - RPRT TI - Letter Circular 570: standards and specifications for buildings and construction materials, fixtures, supplies, and equipment (superseding Letter Circular 323) PY - 1939 PB - National Institute of Standards and Technology CY - Gaithersburg, MD SN - LCIRC 570r1939 DO - 10.6028/NBS.LCIRC.570r1939 ER -