Bolt, Screw and Anchor Coatings Compared: Galvanised, Zinc and Other Finishes

Key things to remember

The essentials from this document in plain words. Check the full document before you rely on a figure.

• ✓Hot dip galvanised (HDG, AS/NZS 1214) and mechanically galvanised (MGAL, ISO 12683) are both 50µm thick and rated high. HDG is recommended for long term outdoor use.
• ✓MGAL resists abrasion better than HDG, gives similar corrosion resistance and carries no risk of hydrogen embrittlement. Zinc flake silver (ZFS, ISO 10683, 10µm, high) also avoids hydrogen embrittlement, and is thin enough to fit a standard internal thread with no over-tapping.
• ✓Zinc plated (Z/P) and zinc yellow passivate (ZYP), both ISO 4042 and 5µm, are rated low. Z/P is for indoor and noncorrosive places; ZYP resists corrosion better and suits low-corrosion places or temporary fixing.
• ✓Self-drilling screws: Class 3 (AS/NZS 3566.2, 21µm, moderate) is for mild, moderate industrial or marine environments, corrosivity categories C2 and C3 to ISO 9223. Class 4 (38µm, high) is for severe marine environments, category C4.
• ✓TYKOTE (38µm, high) is formulated to resist treated pine chemicals. R1000 and R1500 are zinc with a hard ceramic top coat for products that need significant abrasion resistance.
• ✓Petrochemical coatings: cadmium (ASTM B-766, 12µm, moderate), 1PX1 moly (10µm, moderate) and Xylan blue or green (25µm, high). 1PX1 and Xylan cut friction for evenly tensioned fasteners and make a good undercoat for epoxy paints.
• ✓Plain (PLN) has no added coating. It is supplied lightly oiled to stop rust in the packaging and help installation.

Who it helps: Anyone choosing a finish for a fastener outdoors, near the coast, in treated pine or in petrochemical work.