Providing, laying, cutting, jointing, testing and disinfecting G.l. pipe line in trenches, with socket joints, using G.l pipes of B.S.S. 1387-1967complete in all respects with specials and valves:- ii) Medium Quality (Provisional) b) 3/4"i/d (20 mm) 2.65mm thick c) 1" i/d (25 mm) 3.25mm thick