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SPAX stainless or yellow zinc: which screw outside

Updated: 22 October 2026

You know the length, and the open question is whether a yellow SPAX screw can live outside. SPAX stainless or yellow zinc is four promises, not two colours of the same screw. YELLOX, WIROX, A2 and A4 do not swap, and none of the yellow boxes here is a decking screw. The listings are the [SPAX screws comparison](/hub/screws-and-accessories/spax-screws). Peter F., DIY & tools editor, set the condition from SPAX GB pages and these amazon.co.uk cards, not from a salt-spray test, on 21 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You know the length, and the open question is whether a yellow SPAX screw can live outside. SPAX stainless or yellow zinc is four promises, not two colours of the same screw.

Our top picks

SPAX SPAX A2 4 x 40 mm

Best overall

SPAX SPAX A2 4 x 40 mm
9.0/10about £20.02
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SPAX SPAX YELLOX 4 x 30 mm

Best value

SPAX SPAX YELLOX 4 x 30 mm
8.6/10about £4.27
View offer
SPAX SPAX assortment 245

Alternative

SPAX SPAX assortment 245
7.4/10about £20.80
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On this page
  1. 1.What the yellow boxes actually are
  2. 2.WIROX is the sheltered middle, and it is not in this set
  3. 3.A2 when the weather is direct
  4. 4.A4 when it is coastal, and decking is separate

What the yellow boxes actually are

YELLOX is coated steel for interior work and construction that stays protected. It is not a stainless alloy, and a scratch that reaches the steel can rust where water sits. The 4 x 30 mm card says powder coated while the title says yellow zinc. The 245-piece colour field says gray. A fence repair in a UK review does not promote YELLOX to an outdoor rating. If rain will sit on the head, you have left this section. Length and drive come first on the SPAX screws buying guide.

WIROX is the sheltered middle, and it is not in this set

WIROX sits between yellow zinc and stainless, and you cannot buy it from these five titles. SPAX's lexicon puts it at about 10 μm for sheltered timber that is not freely rained on, and says WIROX does not replace stainless. Those yellow titles are YELLOX. A cylinder-head C4 WIROX decking screw is on the GB site and it is not an ASIN here. If a drawing names WIROX or C4, you are in a different catalogue. When rain reaches the head, that limit sends you to stainless.
SPAX SPAX A2 4 x 40 mm

Testsieger

SPAX SPAX A2 4 x 40 mm
9.0/10about £20.02
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A2 when the weather is direct

A2 is the stainless answer for direct weather away from salt and acids. In this set that box is B000VD9T6M, 4 x 40 mm, partial thread, about £20.02, 4.8 from 4,208 ratings. The bullet says directly weather-exposed. If you need 30 mm or 50 mm in stainless, the length is wrong. Who should skip it is on best SPAX screws.

A4 when it is coastal, and decking is separate

A4 is the coastal grade. Nothing in this comparison is A4, so a seafront fence is not filled by the A2 box just because it is stainless. SPAX GB lists cylinder-head decking screws in A2, A4 and C4 WIROX. The A2 screw here is a flat countersunk universal, not that decking head. The lexicon notes that stainless against galvanised steel, with water, attacks the galvanised bracket. Keep the metals in one family when the joint stays wet. Dry interior stays YELLOX. Direct rain at a measured 40 mm is the A2 box in this set. Coast or a walked deck is a different range.

Common questions

Can yellow SPAX screws go outside?
Not where rain will sit on them. YELLOX is coated steel for interior and protected construction. A review that used 4 x 30 mm screws on fence repairs does not change that. The box that says directly weather-exposed is the stainless A2 4 x 40 mm pack. A permanently sheltered spot is a WIROX question, and WIROX is not in this set.
What is WIROX for, if it is not on these boxes?
WIROX is the sheltered coating, about 10 μm on the lexicon, for timber that may be damp and is not in direct weather. SPAX says it does not replace stainless. You buy it by finding WIROX on the packet. The yellow boxes here are not that coating, and the C4 WIROX decking screw on the GB site is a different product from all five.
A2 or A4 near the sea?
A4 near the sea. A2 is for direct weather with a stated low resistance to salt water and acids. The only stainless screw in this comparison is A2, 4 x 40 mm, so a coastal job is not filled by that box just because it is stainless. Salt air is where you leave this comparison.
Is the 4 x 40 mm A2 box a decking screw?
No. It is a flat countersunk universal with a partial thread, titled for exterior weather, at about £20.02. SPAX decking screws on the GB category are cylinder-head A2, A4 or C4 WIROX, and none of those is in the five. Both can be outdoor products and still be different heads and different jobs.
Will a coating scratch through to rust, and does stainless do that?
A zinc coating can rust where a scratch reaches the steel and water stays, which is why SPAX keeps YELLOX off direct weather. Stainless A2 does not rely on that plated layer, and it still carries the maker's warning on salt and acids. A4 is the grade those harsher sites are pointed at, and it is not in this comparison.
Why did a UK review use yellow screws on a fence?
Because a buyer chose to. The review sits on the 4 x 30 mm listing next to loft chipboard and flooring. It shows what they attempted, not a corrosion class. The A2 listing is the one whose bullet says directly weather-exposed. Copy the bullet, not the most adventurous review.
Can you mix an A2 screw into a galvanised bracket?
Only if you accept contact corrosion where water is present. Stainless against galvanised steel attacks the less noble metal, the bracket, not the A2 screw. Indoors and dry, the couple matters less. In rain, match the metals or plan to maintain the bracket. The A2 screw in this set does not become galvanised because the bracket is.

Related pages

How to use SPAX screws

SPAX screws

Best SPAX screws: the box for the job, and who skips

SPAX screws buying guide: finish, thread, then bit

SPAX screws for chipboard: 30 mm, 50 mm, or SPAX-M

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk lines in the display file. There is no laboratory test, no salt-spray test, and no pull-out value. A yellow assortment is not treated as ETA-12/0114.

  1. SPAX universal screw, WIROX page (retrieved 22 October 2026)
  2. SPAX technical lexicon (retrieved 22 October 2026)
  3. SPAX stainless A2 universal (retrieved 22 October 2026)
  4. SPAX UKCA (retrieved 22 October 2026)
  5. ETA-12/0114 (15 October 2024) (retrieved 22 October 2026)
  6. GOV.UK construction products (retrieved 22 October 2026)
  7. HSE wood dust (retrieved 22 October 2026)
  8. Screwfix screws buying guide (retrieved 22 October 2026)