China special bolt factory
China special bolt factory CURVED TUNNEL BOLTS ITEM: CURVED TUNNEL BOLTS FOR SUBWAY AND METRO MATERIAL: BOTH LOW CARBON AND MEDIUM CARBON STEEL DIMENSION: ANSI/ASME B18.2.1 HEX BOLTS AND SCREWS FINISHING: BLACK ZINC PLATED YELLOW ZINC PLATED HOT DIP GALVANIZED Material Carbon steel,alloy s