proven practices shall be followed unless otherwise approved by theEmployer. Some relaxation of the following provisions may be permittedwhere equipment is hermetically sealed but it is preferred that tropical gradematerials should be used wherever possible:Metals: fron and steel are generally to be painted or galvanised asappropriate. Indoor parts may alternatively have chromium or copper-nickelplating or other approved protective finish. Small iron and steel parts (otherthan stainless steel) of all instruments and electrical equipment, the cores ofelectromagnets and the metal parts of relays and mechanisms shall betreated in an approved manner to prevent rusting.Screws, Nuts, Springs, Etc.: The use of iron and steel