What is the difference between zinc-plated and hot-dip galvanised fixings?

Zinc-plated fixings have a thin zinc coating (5-12 microns) for light corrosion protection — suitable for indoor use. Hot-dip galvanised fixings have a much thicker coating (45-85 microns) providing substantially better corrosion resistance — specified for outdoor, exposed or coastal environments and structural applications.

What grade of stainless steel fixings should I use outside?

For normal outdoor environments, Grade 304 (A2) stainless steel provides excellent corrosion resistance. For coastal, marine or chloride-rich environments, Grade 316 (A4) is required — it contains molybdenum providing significantly better resistance to chloride-induced pitting corrosion.

What are self-drilling screws?

Self-drilling screws (Tek screws) have a drill-bit shaped point that cuts through material and forms a thread simultaneously — no pilot hole required. Used primarily for fixing metal to metal (roofing sheets, structural steel) and metal to wood applications.

What torque should I use for stainless steel fixings?

Stainless steel fixings are prone to galling (thread seizure). Apply anti-galling compound and use the lower end of the recommended torque range. Approximate torques: M6 A4 ≈ 7-8 Nm, M8 ≈ 18-19 Nm, M10 ≈ 35-37 Nm, M12 ≈ 60-63 Nm.

What bolt grade should I specify for structural connections?

Grade 8.8 bolts are the standard for structural steel connections. For high-strength joints or where space is limited, grade 10.9 allows smaller diameter bolts for the same clamping force. Grade 4.6 is used for light, non-structural connections. Always refer to Eurocode 3 for precise structural calculations.