Screwdriver Bits Explained: PZ2 vs PH2, Torx, and Which Bit for Which Screw

Put the wrong bit in a screw and the screw is ruined before it's halfway home. The bit rides up out of the recess, spins, and grinds the cross in the head into a shallow round dish that no bit will ever grip again. Now you have a screw you can neither drive nor remove, sticking out of a door lining or a kitchen carcass. Almost every stripped screw head comes down to one of two causes: a Phillips bit in a Pozidriv screw (or the reverse), or a bit that wore out a hundred screws ago.

Bits cost almost nothing. They're also the one part of the drill kit that decides whether a screw goes in cleanly.

What a screwdriver bit is, and what drives it

A screwdriver bit is a short steel insert with a shaped tip on one end and a six-sided shank on the other. The shank is 1/4in hex, the same across every brand, and it drops into three tools: the quick-change holder on a combi drill, the collet (the spring-loaded socket on the nose) of an impact driver, or the handle of a multi-bit hand screwdriver.

The tip is the part that matters. It has to match the recess in the screw head (the shaped hole the bit sits in) in two ways: the drive type, meaning the shape of the recess, and the size, meaning how big that shape is. A PZ2 bit is Pozidriv type, size 2. A TX25 bit is Torx type, size 25. Get either one wrong and the bit only touches the recess at a few points, which is exactly how heads get stripped.

The failure has a name: cam-out. Under torque, the bit climbs up and out of the recess instead of turning the screw. A little cam-out on the last quarter turn happens. Cam-out on every screw means the wrong bit, a worn bit, or poor technique.

The drive types you'll meet on a UK build

Pozidriv comes in five sizes, PZ0 to PZ4. The two ends of that range rarely turn up on a house. You'll use PZ1, PZ2 and PZ3, and PZ2 does most of the work.

Pozidriv vs Phillips: the trap nearly everyone falls into

This is the mistake that ruins more screw heads than any other, and it happens because the two drives look almost identical at arm's length. Both are a cross. Both come in size 2. Shops still sell bit sets weighted towards Phillips, even though the screws you'll drive on a UK timber job are overwhelmingly Pozidriv, a complaint UK trade channels have been making for years.

To tell them apart, look closely at the screw head. A Pozidriv screw has four small lines stamped in the head, set at 45 degrees between the main slots, so the recess looks like a cross laid over a faint star. A Phillips screw is a plain cross. The bits carry the same difference: a PZ bit has small extra ribs between the four main blades, while a PH bit has four blades only, tapering to a sharper point.

The shape of those blades is why the pairing matters. Phillips blades taper, so under load the bit tends to ride up the sloping walls of the recess and lift out. Pozidriv blades have straighter, near-parallel sides and the extra ribs add contact, so the bit stays seated at higher torque. Whether Phillips cam-out was a deliberate design choice is argued about. What it does to a screw isn't.

Put a PH2 bit in a PZ2 screw and it contacts too few of the drive surfaces and spins out. Put a PZ2 bit in a PH2 screw and it sits at the wrong depth, with the same result. Neither combination "nearly works". Match them.

Click to enlarge

What bit for which screw

This is the lookup most people actually want, and for Pozidriv and Phillips it's fixed by the screw's diameter. The sizes below match the wood screws guide, which is the reference for gauges and lengths.

The short version: PZ2 drives every screw in the 3.5-5.0mm range, which is most of the screws on a build. PZ3 takes over at 6.0mm and above. PZ1 is for the fiddly small stuff below that. It's why a PZ2 bit wears out long before anything else in the case.

Pilot and clearance holes come first, and their sizes are set by the screw diameter too. The drill bits guide has the full pilot hole table.

Torx: read the box, not a chart

Torx sizes don't map neatly onto screw diameter the way Pozidriv does. Two 5mm decking screws from different brands can need different bits, and general "rough guide" tables disagree with screw manufacturers about the manufacturers' own products. Any chart that confidently says "5mm screw, TX25" is guessing.

The size is printed on the box, and many boxes of decking or structural screws include a matching bit. Keep that bit in the box for the length of the job. TX20 and TX25 are the two sizes that turn up most often on construction screws, which is why both belong in a starter kit, but confirm against the box before you drive the first one.

The upside of Torx is real. The six-lobed star holds the bit far better than a cross, so cam-out is rare and long structural screws drive without the bit jumping. The 7.5mm concrete screws used as frame fixings are Torx drive as well, and again the size is brand specific.

Bit length and holders

25mm insert bits are the standard: short, stiff and cheap. They sit in a holder rather than directly in the tool.

50mm power bits go straight into an impact driver or a combi's hex holder with no extension. The extra length helps you see the screw and reach into corners, such as inside a kitchen carcass.

90mm and longer bits reach screws at the back of a deep unit or down between joists. Long bits flex more, and cheap long-bit sets have a poor reputation among trades. The better answer is a long holder with a good short bit in it.

A magnetic bit holder is the cheapest upgrade in this whole category. It holds a 25mm bit, grips the screw magnetically so you can start it one-handed, and the better ones have a sliding sleeve that wraps around the screw and keeps it straight as it starts. Expect £6.99 – £15.99 for a decent one. For plasterboard, a bit with a depth-stop collar sets the screw depth far more reliably than waiting for a PH2 to cam out at the right moment.

Impact-rated vs standard bits

An impact driver doesn't just turn the bit. It hammers it round, with thousands of sharp rotational strikes a minute. A standard bit is hardened for smooth, continuous rotation in a drill, and under that repeated shock it fatigues fast: it snaps, the tip rounds off, or it starts camming out of every screw.

Impact-rated bits have a torsion zone: a visibly narrower, often darker section of shank behind the tip. It twists slightly on each blow and absorbs the shock that would otherwise crack the tip. Look for "impact" on the packet. DeWalt FlexTorq, Bosch Impact and Makita Impact Black are the names you'll see at Screwfix and Toolstation.

Impact-rated bits work in a combi drill too. If you own both tools, buy impact-rated only and stop worrying about which bit went in which tool.

How to drive a screw without stripping it

Most stripped heads come from technique as much as the bit. Five habits fix nearly all of it.

How to tell a bit is worn out

Bits wear faster than anyone expects. On a PZ2 or PH2, the blades should have crisp, square edges and a defined point. A worn bit has rounded, polished-looking edges and a blunted tip, and it cams out on screws that went in perfectly with a fresh one.

The field test is simple. If screws that were driving cleanly start slipping near the end of each drive, change the bit before you blame the screws.

There's no reliable figure for how many screws a bit lasts. One tradesperson on DIYnot, driving hundreds of 5mm screws a day into structural softwood, reported standard bits lasting anywhere between a whole morning and half a dozen screws. That spread is why trades buy PZ2 bits by the 25-pack.

Keep a new PZ2 and a new PH2 in reserve at all times. A fresh bit costs pennies. A stripped screw in a finished kitchen carcass costs a lot more than that.

Quality: is it worth paying more?

Most decent bits are made from S2 tool steel, printed on the packet or the case. That's a reasonable baseline to look for.

Coatings are marketing as often as engineering. A titanium coating (the gold colour) can hide poor-quality steel underneath, a caution Screwfix's own buying guide makes. Diamond-grit tips are sold on the promise of extra grip in the recess.

Whether premium bits pay off depends on volume. Trade forums on DIYnot and MoneySavingExpert keep reaching the same conclusion: Wera Impaktor and Wiha bits outlast the rest under heavy impact use, and the same regulars call them expensive. For a homeowner driving a few hundred screws on a project, a mid-range impact-rated set from DeWalt or Bosch is plenty, as long as you replace bits as they wear.

What to buy

Skip the 100-piece case. As with drill bits, most of it never leaves the box, and the sizes you actually use run out first.

Budget. A small pack of 10-25 standard bits in PZ2 or PH2 from Erbauer, Abracs or a generic brand costs £1.59 – £9.99. Fine for a combi drill and occasional work, but not for an impact driver.

The sensible buy. An impact-rated S2 steel set from DeWalt or Bosch costs £17.99 – £29.99. It covers the PZ, PH and TX sizes on the table above, it works in both tools, and it's the set to put in the case at the start of a build. Top it up with packs of impact-rated PZ2 and PH2 bits as they wear, at £2.79 – £7.99 a pack.

A hand screwdriver. A multi-bit ratchet screwdriver takes the same 1/4in bits and costs £7.50 – £20.89 for an entry-level Draper. It's the right tool for adjusting hinges, fitting small hardware and anywhere a power tool would overdrive the screw.

External resource

Screwfix screwdriver bits

Standard and impact-rated bits from Erbauer, DeWalt, Bosch and Wera, sold in small packs and full sets.

screwfix.com

External resource

Toolstation screwdriver bits

Impact-rated PZ2 and PH2 packs and bit sets, including DeWalt FlexTorq and Bosch Impact.

toolstation.com

What a project-managing homeowner actually needs

Even if your trades bring their own kit, you'll be assembling flat-packed units, adjusting hinges, fixing snags and screwing down the odd loose board for the whole length of the job. This kit covers nearly all of it:

• PZ2 x 25mm, three bits. The workhorse. You'll get through these.
• PZ2 x 50mm, one bit. For reaching into kitchen carcasses and corners.
• PZ1, one bit. Hinges, drawer runners and small hardware.
• PZ3, one bit. Screws of 6mm and above.
• PH2 x 25mm, two bits. Drywall screws and Phillips-head hardware only.
• TX20 and TX25, one of each. For decking and construction screws, once you've checked the box.
• A magnetic bit holder with a sliding sleeve. Holds the screw straight while it starts.
• A multi-bit ratchet screwdriver. For the jobs where a power tool is too much.

That's ten bits, all impact-rated, plus two holders. Buy them before the kitchen carcasses arrive, not halfway through a run of wall units.

Where you'll need this

Screws get driven at nearly every stage of any extension or renovation project:

• Insulation - timber battens over the internal layer of PIR, ahead of the plasterboard
• Plastering - PH2 bits for boarding stud walls and ceilings before the skim
• Kitchen installation - cabinet connectors joining the base carcasses, and wall units hung on mounting plates screwed to the wall

Keep a spare PZ2 and PH2 in the case at every stage. A worn bit is the cheapest problem on the build to fix, and the easiest one to ignore until it has stripped a screw.

Where to buy Screwdriver Bits

DeWalt DT70702 40-piece impact-rated screwdriver bit set in tough case Impact-rated PZ, PH and Torx bits in the sizes the page covers, so one set fits a combi drill and an impact driver.

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