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

Updated: 22 October 2026

You are fixing chipboard, an MDF shelf, an OSB panel or a furniture carcass, and the screw may be a general SPAX universal rather than a panel screw. A universal YELLOX screw can go into those boards, with the maker's limit on pre-drilling, and it is not SPAX-M. This page stays indoors. Prices are the [SPAX screws comparison](/hub/screws-and-accessories/spax-screws). Peter F., DIY & tools editor, wrote this from SPAX GB pages and the UK reviews, not from a panel test, on 21 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You are fixing chipboard, an MDF shelf, an OSB panel or a furniture carcass, and the screw may be a general SPAX universal rather than a panel 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
View offer
SPAX SPAX YELLOX 4 x 50 mm

Alternative

SPAX SPAX YELLOX 4 x 50 mm
8.2/10about £18.95
View offer
SPAX SPAX YELLOX 4 x 30 mm

Best value

SPAX SPAX YELLOX 4 x 30 mm
8.6/10about £4.27
View offer
On this page
  1. 1.Universal screw or SPAX-M
  2. 2.30 mm, 50 mm, and the board you are fixing
  3. 3.Full thread does not always clamp two sheets
  4. 4.When a furniture screw is the wrong fastener

Universal screw or SPAX-M

A universal screw is the ordinary countersunk SPAX for timber and boards, including chipboard, MDF and OSB, depending on the wood. The indoor matches here are YELLOX 4 x 30 mm, B0057WZEIY, at about £4.27, and 4 x 50 mm, B0057XFTYM, at about £18.95. SPAX-M has a CUT point, a small head, partial thread, WIROX, and at least 25 mm from an MDF edge. Screwfix lists a 4.5 x 50 mm MDF pack at £17.49 including VAT. That is another shop, not an ASIN here. If the drawing says SPAX-M, you are not looking at B0057WZEIY.

30 mm, 50 mm, and the board you are fixing

A 30 mm screw through 18 mm chipboard leaves about 12 mm in the joist. That is a modest bite, and too much if you are only joining two thin sheets. Screwfix's rule of thumb is at least half the piece you are biting into. Length order is the SPAX screws buying guide. The 4 x 50 mm box leaves about 32 mm after an 18 mm panel. It will spear a second 18 mm board. One review mentions 35 mm, so look at a screw on arrival.
SPAX SPAX A2 4 x 40 mm

Testsieger

SPAX SPAX A2 4 x 40 mm
9.0/10about £20.02
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Full thread does not always clamp two sheets

Full thread can hold two sheets apart if it grips the top sheet. The clamp is a clearance hole, which how to use SPAX screws walks through. The 30 mm and 50 mm boxes are full thread. The A2 4 x 40 mm screw is the partial-thread stainless clamp. Near an edge, try scrap first.

When a furniture screw is the wrong fastener

A carcass screw is the wrong fastener when the board is structural, or when a metal connector is in the joint. SPAX says use its wood-connector screws on OSB and chipboard, with the tip through the board. ETA-12/0114 does not turn the about £4.27 box into that fastener. These are wood and panel screws. Masonry wants a plug matched to its screw.

Common questions

Can you use ordinary SPAX universal screws in chipboard?
Yes, with the maker's limit. The universal page includes chipboard, MDF and OSB without pre-drilling, depending on the wood. The indoor options in this set are the 4 x 30 mm and 4 x 50 mm YELLOX boxes. They are not SPAX-M. A pilot is still sensible near an edge. One plywood review drilled 3 mm even on the stainless box.
What is SPAX-M, and is it in this comparison?
SPAX-M has a CUT point, a small head, partial thread and WIROX, and SPAX states at least 25 mm from an MDF edge. None of the five amazon.co.uk boxes is that screw. Screwfix has listed a 4.5 x 50 mm MDF pack at £17.49 including VAT, which is another shop and not a row here. The 25 mm figure stays with SPAX-M.
30 mm or 50 mm for loft boards?
Use 30 mm when the board is about 18 mm and about 12 mm of bite into the joist is enough, which is what the loft reviews on the about £4.27 box point at. Use 50 mm when that bite is short or you are fixing a bracket through 18 mm ply. Do not use 50 mm to laminate two thin boards if the tip will come out of the back.
Will full thread pull two sheets tight?
Not reliably. Full thread grips the top sheet and can hold a gap open. The 30 mm and 50 mm YELLOX boxes are full thread. A clearance hole in the top sheet lets the thread pull only in the sheet behind. In this set a plain shank is on the stainless 4 x 40 mm screw, or on SPAX-M, which is not in the table.
How close to an MDF edge is the maker's SPAX-M figure?
At least 25 mm, on the SPAX-M page, for that screw. Do not copy 25 mm onto the universal YELLOX boxes. If you are close to an MDF edge and you want the screw that figure was written for, you want SPAX-M, not the 4 x 30 mm box. Stay well in from the edge if you use a universal screw, and still try a scrap piece.
Are these screws for wall plugs behind a cabinet?
No. They are wood and panel screws. A cabinet on masonry needs a plug and a screw specified for that plug. The bit kit mentions chipboard and thin sheet metal, not a masonry anchor. A 4 x 30 mm universal screw in a plug hole is the wrong fixing even if the head looks tidy.
When is a furniture screw the wrong fastener for a floor that carries load?
When the floor or the connector is structural. ETA-12/0114 covers specified screws into particleboard and OSB. It does not turn the about £4.27 box into that screw. Connector plates take SPAX wood-connector screws, with the tip through the back of the board. Pinning a dry loft panel to a joist can stay with the universal screw. A hanger that names an ETA screw cannot.

Related pages

Best SPAX screws

SPAX screws

SPAX screws buying guide: finish, thread, then bit

How to use SPAX screws: the bit, the pilot, the clamp

SPAX stainless or yellow zinc: which screw outside

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)