Usually more than current 3000A before considering the use of copper or stainless steel bolts titanium screws. Generally not allowed inside the transformer is usually galvanized bolts, bolts galvanized surface layer with a long soak in the transformer oil will produce chemical changes, on the one hand to produce metal ions affect the insulation, on the one hand will lead to deterioration of the oil, so to use the surface of hair black bolt handle, not a last resort do not use galvanized bolts. Titanium screws when used in securing large current flows copper bar, in order to avoid local overheating of the bolt, the bolt may be a lower copper or copper bolt strength, especially brass bolt, more brittle, easily broken, based on experience, available bis Copper head studs instead. Copper is not used in order to reduce the resistance of the bolt, and in fact, the purpose of using the same stainless steel bolts, copper and stainless steel titanium screws are relatively poor magnetic properties of the material, eddy current loss generated in the leakage magnetic field of the transformer is small, easy to heat. When fastened with a large current flows in the copper bar, in order to avoid local overheating of the bolt, the bolt may be copper or a copper bolt strength is low, especially brass bolt, more brittle, easily broken, based on experience, available stud copper studs instead. Stainless steel titanium screws because of its material properties, more "sticky" and once again is not easy fastening demolition, so to an ample supply of spare parts, need to be removed when the original bolts should be destroyed, and back to new.