copper alloy. Ferrous nails shall be hot-dip galvanized steel. 4. Plastic Cement: Plastic cement shall conform to the requirements of Federal Specification 8S-C-153. 5. Serews: Screws shall conform to the requirements of Federal Specification FF-S-111 and shall be of the type hereinefter specified or required to pro- perly secure the work. Non-ferrous screws shall be hard copper or copper alloy, or hard aluminum alloy as required, ferrous screws shall be of steel, galvanized. 6. Solder: Solder shall conform to the requirements of Federal Specification QQ-S-571lb, Class A. Flux shall be rosin except where prohibited by unusual conditions of application, in which event soldering flux paste conforming to the requirements of Federal Specification O-F-506, or muriatic acid properly killed with zinc may be used. 7. Soldering Flux: Soldering flux shall COoe to the requirements of Federal Specification O-F-50 ° b. Soldering: All edges of sheet metal to be soldered shall be pretinned before soldering is begun. Soldering shall be done slowly with well-heated coppers so as to thoroughly heat the seam and completely sweat the solder through the full width of the seam. Ample solder shall be used and the seam shall show not less than one full inch of evenly flowed solder. Where soldering paste or killed acid is employed as a flux, scldering shall follow immediately after application of the flux. Upon completion of soldering, surfaces shall be thoroughly cleaned. c. Seams: 1. Flat lock seams shall finish not less 2. Solder lap seams shall finish not less 3. Unsoldered plain lap seams shall not lap than 3/4 inch wide. than one inch wide. less than 3 inches. 11-3