Mild Steel vs High Tensile Bolts
High tensile bolts are hardened and tempered and carry far more load than mild steel bolts. Use high tensile bolts for structures, machinery and vehicles; mild steel bolts only for light, non-critical fixing.
Strength
High tensile bolts are made from medium carbon or alloy steel and heat treated. They resist stretching under load, so the joint stays tight. Mild steel bolts stretch and loosen under heavy or vibrating loads.
How to identify them
High tensile bolts carry a grade marking on the head. Mild steel bolts are usually unmarked or carry a low grade marking.
Matching nuts and washers
A high tensile bolt needs a matching high tensile nut and a hardened washer. A soft nut or washer becomes the weak link.
When mild steel is fine
Gates, grills, furniture, racks and light brackets can use mild steel bolts, which cost less and are easier to galvanize.
