Every screw in a PC and a laptop, and the driver that fits it.

Almost every screw in a desktop PC is one of two threads: #6-32 UNC, an imperial thread for the case, power supply and big hard drives, or M3, a metric thread for SSDs and optical drives. The two look nearly identical and don’t mix. M.2 drives use a tiny M2 screw, fans use coarse self-tapping screws, and laptops are built almost entirely from M2 and M2.5 screws in several lengths, turned by Phillips, Torx or pentalobe drivers depending on the brand. Get the thread right, the length right and the driver right, and nothing strips.

How a screw is described

Every screw has four things that matter: the thread (how wide it is and how close together the ridges are), the length, the head shape, and the drive, the pattern in the head that the screwdriver fits. Two screws can share a thread and differ in everything else, and in a laptop that difference matters.

The five threads you will meet

Five threads cover nearly every screw in a computer. Drawn at the same scale, the difference between them is clear; in the palm of your hand it isn’t, which is why M3 and 6-32 get mixed up so often.

Smaller still, M1.6 and M1.4 turn up in laptop keyboards, phones and tablets. UNC stands for Unified National Coarse, the American thread standard; the “M” threads are ISO metric. The PC kept the American threads because the original IBM PC and its drives were designed in the United States, while 2.5-inch drives, optical drives and M.2 came later, from a metric world.

Telling M3 from 6-32

• Put two side by side, thread to thread. If the ridges line up all the way along, they’re the same thread. If they drift out of step after a few ridges, they aren’t. This is the quickest test there is.
• Look at the head. A chunky hex head with a Phillips cross in it is almost always 6-32. A thin, flat head on a short screw is usually M3.
• Use a thread gauge. A cheap screw-pitch gauge or a nut-and-bolt checker board settles it in seconds and earns its place in any parts drawer.
• Feel it. An M3 in a 6-32 hole turns freely and wobbles. A 6-32 started in an M3 hole bites for about a turn and then gets stiff. Stop there: one more turn cuts a new, wrong thread into the part.

Desktop PC screws, part by part

Here is where each screw lives in a typical tower, seen from the side with the glass panel off: the back of the case is on the left, the front on the right.

1. 1Motherboard: 6-32 screws into brass standoffs (M3 in some cases)
2. 2M.2 SSD: one M2 × 3 screw on an M2 standoff
3. 3CPU cooler: the cooler kit’s own screws or thumb nuts
4. 4Card bracket: 6-32 hex screw or thumbscrew
5. 5Power supply: four 6-32 × 1/4″ from the back
6. 63.5″ hard drive: 6-32, side or bottom holes
7. 72.5″ SSD: short M3 screws
8. 8Case fans: self-tapping, about 5 × 10 mm
9. 9Radiator: M3 (sometimes M4 or 6-32); length matters
10. 10Side panel: 6-32 knurled thumbscrews

Things the table doesn’t tell you

• The hex-head 6-32 is the classic “PC screw”: a 1/4-inch flanged hex head with a Phillips cross in it, so a #2 screwdriver or a 1/4-inch nut driver both work. The flange spreads the load on thin case steel.
• 3.5-inch drives have two sets of holes: three on each side and three or four underneath, all 6-32. Tool-free drive trays use shouldered pins or rubber-grommet screws in the same holes to soak up vibration.
• 2.5-inch drives want short screws. A screw longer than about 4 mm can bottom out in the hole before the head is tight, or press on the drive’s circuit board. Use the ones from the drive or case bag.
• D-sub jackscrews on VGA and serial plugs are #4-40, the one imperial thread smaller than 6-32. The hex posts they screw into snap off if overtightened.
• Rack equipment such as servers, switches and patch panels in Australian racks almost always uses M6 screws into square cage nuts. Some American racks have tapped 10-32 or 12-24 holes instead, and those screws don’t mix with M6 either.

Standoffs: why the motherboard floats

A motherboard has hundreds of solder joints on its underside. Screwed flat against the steel tray, they would short out. Standoffs hold it about 6.5 mm above the metal, and the screws that hold the board down go into the standoffs, not the case.

• The common standoff is brass, 6-32 male thread below and 6-32 female above, with a 5 mm or 3/16-inch hex body. Some take an M3 screw on top. Many cases ship with them already fitted for ATX, and include a little socket to drive extra ones.
• Mini-ITX and micro-ATX boards use a subset of the ATX holes, so a case may have more standoffs fitted than your board needs. Move or remove the extras.
• A centre “locator” standoff in many cases has a raised pin instead of a thread. It holds the board in place while you start the other screws.
• Plastic snap-in standoffs exist and turn up in old or cheap cases. They hold, but not as firmly.

M.2 screws

An M.2 drive plugs into an angled slot and is then pressed flat and held down by one small screw at its far end. The screw is M2 × 0.4, usually 2 to 3 mm long with a thin wafer head, and it screws into a little M2 standoff fitted at the position matching the drive’s length.

• Lengths vary: most boards use M2 × 3 mm, some M2 × 2.5 or M2 × 2. A screw that’s too long bottoms out before it clamps the drive. If you buy spares, check your board’s manual for the length.
• Never force an M3 or 6-32 into an M.2 standoff. It ruins the standoff’s thread in one turn.
• Many recent boards use a tool-free latch instead, a small rotating or push-in clip at the drive’s end. Heatsink covers over the M.2 slots are usually held by their own captive M2 or M3 screws.
• Wi-Fi cards in the M.2 E-key slot (usually 2230) use the same M2 screw.

Fan and radiator screws

Case fan screws are the odd ones out: coarse, self-tapping screws, about 5 mm across and 10 mm long, often listed as “KB5 × 10”. The fan’s plastic corner holes are about 4.3 mm, so the screw cuts its own thread into the frame. Drive them in straight and stop when snug; plastic threads strip easily and can only be cut once or twice. Rubber push-through pins are a quieter alternative.

Radiator screws are machine screws, mostly M3, though Hardware Labs radiators use M4 and some other makers use 6-32. They pass through the fan and into threaded holes in the radiator’s end plates, and here length is everything.

Laptop screws

A laptop is a different world. Nearly every screw is M2 or M2.5, a few are M1.6 or M3, and the same thread comes in several lengths, often from 2 mm to 8 mm in one machine. The screws look identical from the head. The lengths are not interchangeable.

The screw map: the one habit that saves laptops

Put a long screw into a short hole and it keeps going, through the plastic boss and into whatever is behind it: the keyboard, the screen, or the motherboard, where it can cut a track and kill the machine. Repairers call it “long screw damage”, and it is entirely avoidable.

• Captive screws are held in the cover by a small clip or a thread in the cover itself. They loosen but don’t come out, so don’t pull on them: undo every one, then lift the cover from the hinge end. ThinkPad, Latitude, EliteBook and Framework bottom covers all work this way.
• Hidden screws sit under rubber feet, long rubber strips, stickers and the plugs around a screen bezel. If a cover still won’t lift with every visible screw out, check under the feet before reaching for a pry tool.
• Heatsink screws are numbered 1, 2, 3, 4 on the heatsink. Loosen in reverse order and tighten in order, a little at a time, so the cooler sits flat on the processor.
• Blue or orange patches on a screw’s thread are a factory thread-locking patch. It holds a few more times. Don’t add liquid threadlocker near laptop plastics: some kinds crack polycarbonate.
• Brass inserts are the threaded metal sleeves moulded into plastic bases. Overtightened, they spin loose or pull out. That needs a repair (epoxy or a new heat-set insert), not a longer screw.

Which laptop uses which screws

A guide to the bottom covers, as most models in each range ship. Ranges change between generations, so check before you buy a bit for a particular laptop.

Every drive type, and how to tell them apart

The drive is the shape in the head. Most are designed to suit a factory: some to resist the driver slipping out (“cam-out”) under a power tool, some to take more torque in a small head, and a few, frankly, to keep owners out.

Phillips, JIS and Pozidriv

Phillips is the default in computers. Its tapered recess is designed to push the driver out once the screw is tight, which saves the screw from over-driving but strips the head if you don’t press hard enough. JIS (Japanese Industrial Standard B 1012) looks the same but has a recess shaped to hold the driver in. A Phillips tip only touches a JIS recess at its edges, which is why screws in Japanese cameras and laptops strip so easily under a Phillips driver. Pozidriv, common in European woodwork and rare in computers, has four extra ribs; a Phillips driver in a Pozidriv screw slips, and vice versa.

The rule: use the largest tip that fills the recess fully. A tip one size too small is the most common cause of stripped laptop screws.

Torx, security Torx and pentalobe

Torx, the six-lobed star, takes more torque without slipping than any cross-head, which is why premium laptops and hard drives use it. Sizes go by a T number; the computer sizes are small.

• Security Torx (Torx TR, “tamper-resistant”) has a pin in the middle, so only a bit with a hole in its tip fits. You’ll find it on power supplies and other parts with mains voltage inside, where the message is “don’t open this”. A PSU’s capacitors can hold a dangerous charge long after it is unplugged; that message is worth heeding.
• Pentalobe is Apple’s five-lobed head. P5 holds MacBook Air and MacBook Pro bottom cases; the smaller P2 is on the bottom edge of iPhones. A Torx bit will turn one in an emergency and ruin it in the process; buy the bit.
• Tri-wing turned up on the batteries of older MacBook Pros and is common in Nintendo consoles. Tri-point, a symmetrical Y, holds parts inside iPhones from the iPhone 7 onwards and the Apple Watch.
• Hex socket (Allen) screws appear on GPU support brackets, some case panels and radiator kits. M3 socket-head screws take a 2.5 mm key; M3 button heads take 2 mm.

Head shapes

The head shape tells you as much as the thread does about where a screw belongs.

The toolkit

Cheap, mixed-quality bit sets are a false economy: soft bits round over and take the screw head with them. A good precision set is not expensive. What we keep on the bench:

• Phillips #2, a full-size screwdriver with a magnetised tip and a shaft at least 100 mm long, for desktops.
• A precision set with Phillips #000, #00, #0 and #1; Torx T3 to T10, including security bits; pentalobe P2 and P5; tri-wing and tri-point; JIS #00 to #1; and 1.5 to 3 mm hex.
• A 5 mm nut driver for standoffs and D-sub jackposts.
• Plastic spudgers and opening picks, for clips and covers once every screw is out.
• Somewhere to put the screws: a magnetic mat, a parts tray with compartments, or paper and tape for a screw map.
• Spares: a PC screw kit with 6-32 and M3 screws, standoffs and thumbscrews, plus a bag of M2 × 3 screws and M.2 standoffs, covers nearly every lost-screw moment.
• A thread gauge or nut-and-bolt checker, to identify a stray screw in seconds.

When it goes wrong

A stripped head

1. Stop turning. Every slipping turn makes it worse.
2. Check the bit: the right type (JIS, not Phillips; P5, not Torx) and the largest size that fits.
3. Press harder and turn slowly. A square of wide rubber band between the bit and the screw often gives enough grip.
4. Use a screw extractor bit, sold in small sizes for laptop screws. It bites into the damaged head as it turns anticlockwise.
5. Last resort: grip a raised head with fine pliers, or cut a slot with a rotary tool, after covering everything nearby against metal dust. On a laptop this is a job for the bench, not the kitchen table.

A stripped or cross-threaded hole

• In a case: a hole damaged by a 6-32 forced into an M3 thread can usually be re-cut with a 6-32 tap and used with 6-32 screws from then on. In thin case steel, a self-tapping screw of the next size or a rivet nut is the fallback. Never re-tap the holes in a drive; replace the screw with the correct one.
• In a laptop: a spinning brass insert can be glued back with epoxy, or replaced with a heat-set insert. A cracked plastic boss can be rebuilt with epoxy, but it is fiddly work.
• A spare screw left over after reassembly means a hole somewhere is empty. Find it: loose covers creak, and a missing heatsink screw means hot running.

A dropped screw

A loose screw inside a PC or laptop can short two contacts the moment power is applied. Find it before switching on: tilt and gently shake the case, look with a torch, or pick it up with a magnetised screwdriver. Never power up to “see if it’s fine”.

The short version

• Desktops run on two threads: 6-32 for the case, PSU, 3.5″ drives and most motherboards, and M3 for 2.5″ and optical drives. They look alike and don’t mix: if a screw stiffens after one turn, stop.
• M.2 drives take one M2 × 3 screw on a standoff moved to the drive’s length.
• Fans use self-tapping 5 × 10 mm screws. Radiators take M3 (sometimes M4 or 6-32), and a screw that’s too long punctures them.
• One standoff under every motherboard hole, and none anywhere else.
• Laptops are M2 and M2.5 in many lengths. Keep a screw map; a long screw in a short hole can kill the board.
• Match the driver: Phillips #2 for desktops, #0 and #00 for laptops, Torx T5 for many premium laptops, P5 pentalobe for MacBooks, JIS for Japanese brands.

Common questions