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Stainless or coated decking screws: which metal your deck needs

Updated: October 2026

Whether you need stainless or coated decking screws depends on the garden and the timber. Green organic-coated carbon steel is a sensible buy for an inland deck on pressure-treated softwood. Near the coast, or on oak, it is the wrong metal and A4 takes over. Named packs and prices are on the [decking screws comparison](/hub/screws-and-accessories/decking-screws). Figures are October 2026 amazon.co.uk listings, not a lab test. A qualifying purchase through our links can earn a commission at no extra cost to you.

Whether you need stainless or coated decking screws depends on the garden and the timber. Green organic-coated carbon steel is a sensible buy for an inland deck on pressure-treated softwood.

Our top picks

HOME IT HOME IT A4 6 x 100 mm

Best overall

HOME IT HOME IT A4 6 x 100 mm
7.4/10about £13.49
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Forgefix ForgeFix 4.5 x 60 mm

Rank 2

Forgefix ForgeFix 4.5 x 60 mm
9.2/10about £5.84
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TIMCO TIMCO Classic 4.5 x 70 mm

Best value

TIMCO TIMCO Classic 4.5 x 70 mm
8.9/10about £8.50
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On this page
  1. 1.When green-coated carbon steel is the right metal
  2. 2.A2 for general outdoor stainless, A4 for chlorides
  3. 3.Oak and other tannin-rich timber
  4. 4.Salt-spray hours and the only A4 pack in this set

When green-coated carbon steel is the right metal

Green organic-coated carbon steel suits an inland treated-softwood deck. The coating protects against rain and preservative chemicals, and it only works while it stays intact. The TDCA warns that a chewed recess, or a head driven deep into the board, is where corrosion starts. The coated boxes here are ForgeFix 4.5 mm at 50, 60 and 75 mm, at £5.21, £5.84 and £7.51 for 200, and TIMCO Classic at 50 and 70 mm, at £6.66 and £8.50. None is stainless. The ForgeFix 75 mm coating line is a listing claim, not a published test.

A2 for general outdoor stainless, A4 for chlorides

BSSA names A2 and A4 under BS EN ISO 3506. A2 (304-type) suits general outdoor use away from salt. A4 (316-type) resists chlorides, so it is the grade for a coast, an estuary or a deck near gritted roads. Green-coated steel, and A2, corrode faster there. An inland owner who wants to avoid rust streaks can choose A2. Within sight of the sea, go to A4. None of the 11 listings is an A2 decking pack, so that buyer has to look beyond this set.
HOME IT HOME IT A4 6 x 100 mm

Testsieger

HOME IT HOME IT A4 6 x 100 mm
7.4/10about £13.49
View offer

Oak and other tannin-rich timber

Oak tannins stain around ordinary steel and attack the screw, even on an inland deck. TIMCO's In-Dex declaration names green oak as a case for stainless. That does not make TIMCO Classic stainless. Those boxes are green coated carbon steel, like ForgeFix. On a coastal oak deck, choose A4. The TDCA still wants a pilot about 2 mm larger than the shank on every hardwood fixing. Pilots, spacing and head depth are in how to screw down decking boards.

Salt-spray hours and the only A4 pack in this set

Salt-spray hours are a laboratory comparison under ISO 9227, not a count of years in a garden. METALLIXITY and the AJ Timber frame screws quote 1,000 hours. TIMCO's 1,008-hour reports cover the In-Dex range, not Classic or ForgeFix. The only A4 pack is HOME IT, £13.49 for 50 TX20 screws stated as AISI 316. The title says 6 x 100 mm and the spec fields say 4.2 x 55 mm. The 4.9 stars are from 13 reviews, none labelled United Kingdom. Length is in the decking screws buying guide, and named picks on best decking screws.

Common questions

Are green coated decking screws good enough?
Green organic-coated carbon steel decking screws are a reasonable choice for an inland deck on pressure-treated softwood, as long as the coating is not damaged when you drive them. They are not suitable for coastal or estuarine decks, where chlorides attack the steel, or for oak and other tannin-rich timber, which stains and corrodes ordinary steel.
What is the difference between A2 and A4 decking screws?
A2 and A4 are stainless steel fastener grades named under BS EN ISO 3506. A2 is a 304-type stainless that suits general outdoor use away from salt. A4 is a 316-type stainless with better resistance to chlorides, which makes it the grade for coastal decks, estuaries and sites exposed to road salt. A4 usually costs more per screw.
Do I need stainless decking screws near the sea?
Yes. Near the coast, an estuary or anywhere exposed to salt spray, choose A4 (316-type) stainless decking screws. The British Stainless Steel Association describes A4 as the grade for chloride exposure. Green coated carbon steel and A2 stainless are both less resistant in those conditions, and rust streaks from the screw heads are a common result.
What screws should I use for an oak deck?
Use stainless steel screws for an oak deck, and choose A4 if the deck is also near the coast. Oak contains tannins that react with ordinary steel, causing dark stains around each head and attacking the screw. Drill a pilot hole about 2 mm larger than the screw shank on every fixing, as the TDCA recommends for hardwood.
Does 1,000 hours of salt spray mean a decking screw lasts for years?
No. Salt-spray hours come from a laboratory test method described in ISO 9227, and the standard does not turn those hours into a service life outdoors. A higher figure suggests a tougher coating in that test, but it cannot tell you how many years a decking screw will last in a particular garden.
Do TIMCO Classic decking screws have the In-Dex salt-spray rating?
No. TIMCO's published 1,008-hour salt-spray figure applies to its In-Dex organic green range. The TIMCO Classic decking screws on amazon.co.uk are a different listing, green coated carbon steel, and their listings do not show that test result. Do not assume a green coating on one range carries the test figure of another.

Related pages

Screws and accessories

Decking screws

Best decking screws for an inland UK softwood deck

Decking screws buying guide for length, metal and drive

Composite decking screws or clips for hollow boards

How to screw down decking boards and keep them flat

Sources

Public UK sources on deck fixings, stainless grades, salt spray, permitted development and eye protection. Listing prices and star counts are from the amazon.co.uk extracts kept for this comparison on 15 and 16 October 2026. Prices move.

  1. TDCA, Deck fixings FAQ (retrieved 16 October 2026)
  2. TDCA, Metal fixings (retrieved 16 October 2026)
  3. GOV.UK, Permitted development technical guidance (retrieved 16 October 2026)
  4. BSSA, Stainless steel fasteners (retrieved 16 October 2026)
  5. ISO 9227:2017 (retrieved 16 October 2026)
  6. TIMCO, Salt-spray test reports (retrieved 16 October 2026)
  7. Ecodek, Composite screws and clips (retrieved 16 October 2026)
  8. HSE, Using the right type of PPE (retrieved 16 October 2026)