Pinball Screws: Every Size Explained (Inches and mm)

Wondering which screw to put back into your pinball machine? In 90% of cases the answer comes down to three references: #6 and #8 wood screws for the playfield, #6-32 and #8-32 machine screws for the mechanisms, and 3/8"-16 x 2-1/2" bolts for the legs. But be careful: all of these are imperial, not metric. This guide gives every dimension in both systems, area by area, with conversion tables, head types, the right screwdrivers, and what to do when a playfield hole is stripped.

Why pinball fasteners are imperial

Pinball is a Chicago-born industry. Gottlieb, Williams and Bally set their mechanical standards in the 1930s to 1950s, long before Europe standardised on metric ISO. Those standards never changed: a 2024 Stern machine still uses #6-32 screws and 3/8"-16 leg bolts, exactly like a 1965 Gottlieb. That is excellent news for parts availability — pinball hardware is interchangeable across 70 years of production — but a permanent trap for the European restorer with a metric screw set on the bench.

In practice: your local hardware shop will not stock #6-32. You need to order from a pinball specialist, or from a supplier of UNC/UNF fasteners. See the Where to buy in Europe section below.

Reading the American designation: what does #6-32 x 1/2" mean?

An American designation reads in three parts:

• The gauge number (#4, #6, #8, #10): this is the outside diameter of the thread. It is not a direct measurement, it is a series number. The official formula is: diameter in inches = 0.060 + (0.013 × number). So #6 = 0.060 + 0.078 = 0.138" = 3.51 mm. Above #12 you switch to fractions of an inch: 1/4", 5/16", 3/8"…
• The number after the dash (32, 40, 24, 16): this is the number of threads per inch (TPI). The higher the number, the finer the thread. To convert to metric pitch: pitch (mm) = 25.4 ÷ TPI. So 32 TPI = 25.4 ÷ 32 = 0.794 mm pitch.
• The length (x 1/2", x 1-1/16"): length under the head for a pan head, overall length for a countersunk head. 1/2" = 12.7 mm.

A wood screw (sheet metal screw) is written differently: gauge and length only, no TPI — "#8 x 1/2"". Its thread is self-tapping with a very coarse pitch, designed to bite into the playfield plywood.

Full conversion table: inches ↔ millimetres

The table below is the heart of this article. Keep it to hand when you strip a machine down.

US designation	Ø in inches	Ø in mm	Threads / inch	Equivalent metric pitch	Typical use on a pinball machine
#4-40	0.112"	2.84 mm	40 TPI	0.635 mm	Small microswitches, circuit boards, backbox standoffs
#4 (wood screw)	0.112"	2.84 mm	self-tapping	—	Small decorative plates, thin guides
#6-32	0.138"	3.51 mm	32 TPI	0.794 mm	King size no. 1. Post tops, targets, plastics, coil brackets, ramps
#6 (wood screw)	0.138"	3.51 mm	self-tapping	—	Under the playfield (mechanisms, brackets, harnesses); short posts
#8-32	0.164"	4.17 mm	32 TPI	0.794 mm	King size no. 2. Heavy mechanisms, flipper brackets, hinges, cabinet ironmongery
#8 (wood screw)	0.164"	4.17 mm	self-tapping	—	Playfield top: wood rails, ball guides, posts, star posts
#10-24	0.190"	4.83 mm	24 TPI	1.058 mm	Cabinet carriage bolts, heavy hinges
#10-32	0.190"	4.83 mm	32 TPI	0.794 mm	Backbox fixings, locks, structural parts
3/8"-16	0.375"	9.525 mm	16 TPI	1.588 mm	Leg bolts and leg levellers. Universal on almost every machine

Diameters calculated from the ANSI formula (0.060 + 0.013 × gauge) and 1 inch = 25.4 mm. Metric pitch = 25.4 ÷ TPI.

Common lengths converted

• 3/8" = 9.5 mm · 1/2" = 12.7 mm · 5/8" = 15.9 mm · 3/4" = 19.1 mm · 1" = 25.4 mm
• 1-1/16" = 27.0 mm · 1-1/2" = 38.1 mm · 1-5/8" = 41.3 mm · 1-3/4" = 44.5 mm
• 2" = 50.8 mm · 2-1/2" = 63.5 mm · 2-3/4" = 69.9 mm · 3" = 76.2 mm

The metric traps: what "almost fits"

This is the most important point in the article. Here are the false friends:

• #8-32 vs M4: Ø 4.17 mm against 4.00 mm, pitch 0.794 mm against 0.700 mm. An M4 goes in two or three turns in a #8-32 tapped hole, then jams. Many restorers force it at that point — and tear out the thread in the mechanism. Not interchangeable.
• #6-32 vs M3.5: Ø 3.51 mm against 3.50 mm — practically identical! But the pitch is 0.794 mm against 0.600 mm. This is the worst case: the screw engages convincingly and then destroys everything. Not interchangeable.
• #4-40 vs M3: Ø 2.84 mm against 3.00 mm. The M3 is simply too big and will not go in.
• 3/8"-16 vs M10: Ø 9.525 mm against 10.00 mm, pitch 1.588 mm against 1.500 mm. An M10 leg bolt will not fit a pinball leg plate. Do not improvise on the legs — they carry 90 kg of machine. On that subject, see our guide to pinball leg sizes.

Golden rule: the correct screw engages by hand for at least two or three turns without effort. If you need a screwdriver from the first turn, stop.

Which screw goes where: the table by area

Area of the machine	Typical fasteners	Dimensions (inches and mm)
Playfield top — wood rails, ball guides	Pan head wood screws, Phillips drive	#8 x 1/2" (Ø 4.17 mm, length 12.7 mm) — the most common; also #6 x 3/8" (Ø 3.51 mm, 9.5 mm)
Playfield posts (star posts, metal posts)	Combination post stud: wood thread at the bottom, 6-32 machine thread on top	#8 x 1-1/16" with 6-32 top (Ø 4.17 mm, length 27.0 mm)
Short posts	Wood-thread post stud	#6 x 1-1/2" (Ø 3.51 mm, 38.1 mm) or #6 x 1-5/8" (41.3 mm)
Tall posts	Long post stud	Generally #6 x 1-3/4" (Ø 3.51 mm, 44.5 mm)
Plastics, ramps, targets	Machine screws + nyloc nuts	#6-32 x 3/8" to 1" (Ø 3.51 mm, 9.5 to 25.4 mm); #6-32 nyloc nuts
Under the playfield — brackets, harnesses, microswitches	#6 wood screws, #6-32 and #4-40 machine screws	#6 x 3/8" and #6 x 1/2" (Ø 3.51 mm, 9.5 / 12.7 mm); #4-40 x 3/8" (Ø 2.84 mm, 9.5 mm)
Coils / solenoids, flipper mechanisms	Machine screws + nyloc nuts, often hex washer head	Mainly #8-32 (Ø 4.17 mm), lengths 1/2" to 1-1/4" (12.7 to 31.8 mm)
Cabinet — hinges, ironmongery, lock, coin door	#8 wood screws, #10-24 carriage bolts, #8-32 machine screws	#8 x 3/4" (Ø 4.17 mm, 19.1 mm); #10-24 x 1-1/4" (Ø 4.83 mm, 31.8 mm)
Backbox — boards, hinges, lock	#6-32, #8-32, #10-32 machine screws; #8 wood screws	#6-32 x 1/2" (Ø 3.51 mm, 12.7 mm) for boards on standoffs
Legs	Acorn head leg bolts, adjustable levellers	3/8"-16 x 2-1/2" (Ø 9.525 mm, length 63.5 mm), 5/8" acorn head (15.9 mm). Extended version 2-3/4" (69.9 mm). Levellers: 3/8"-16 threaded stem, 2" (50.8 mm) or 3" (76.2 mm)

Note: these values are the most widespread standards (Williams, Bally, Stern, solid-state Gottlieb). Some models — particularly 1960s–70s electromechanical Gottliebs and European licensed manufacturers — depart from them. Always check on your own machine before ordering in quantity.

Head types and where you meet them

• Pan head — the most common. Flat, wide bearing surface, does not mark the playfield. Used for wood rails, star posts, metal posts and under-playfield brackets.
• Flat / countersunk head (82°) — sits flush in a conical recess. Used on the playfield where the ball travels, and on ramps. Note: American countersinks are 82°, metric ones 90°. A metric countersunk screw will not seat properly in an 82° recess.
• Round head / binding head — period style, very common on electromechanicals (EM). An important aesthetic choice if you are restoring to original.
• Hex washer head — driven with a socket or hex bit, with no risk of cam-out. Very common under the playfield and on cabinet ironmongery. On many Williams/Bally machines, the under-playfield wood screws are 1/4" (6.35 mm) hex head.
• Acorn (cap) head — the leg bolts. The closed dome hides the thread; the head is 5/8" (15.9 mm), so a 16 mm socket fits.
• Post stud / T-nut — the combination post fixing: wood thread on one side, 6-32 or 8-32 machine thread on the other.

Drives and screwdrivers: the right size prevents 90% of the damage

The cam-out that wrecks a screw head almost always comes from a screwdriver that is too small.

• Phillips — the vast majority of modern pinball hardware. PH1 for #4 and #6, PH2 for #8 and #10. A PH1 in a #8 head will cam out; so will a PH2 in a #6. Own both.
• Slotted — on older and electromechanical machines. Use a parallel-sided (cabinet tip) blade, not a tapered DIY blade: the tapered one lifts out and widens the slot.
• Hex / socket — for hex washer heads (1/4" = 6.35 mm and 5/16" = 7.94 mm) and leg bolts (5/8" or 16 mm socket).
• Spanners for nuts — #6-32 nyloc nuts generally take a 5/16" (7.94 mm), #8-32 an 11/32" (8.73 mm) and #10-32 a 3/8" (9.53 mm). A slim nut spinner or thin-wall socket is essential on the playfield.

A magnetic screwdriver and a magnetic parts tray will spare you the most tedious part of any restoration: finding a screw that has dropped into the cabinet. See our selection of essential tools for the pinball enthusiast.

Vibration resistance and nyloc nuts: why they matter on a pinball machine

A pinball machine vibrates constantly: coils snap, bumpers fire, the ball hits at 3 m/s. Without a locking feature a machine screw works loose within a few hundred games. That is why nearly all the machine hardware in a commercial pinball machine is in a vibration-resistant version:

• Nyloc nuts (nylon insert lock nuts) — a nylon ring inside the nut grips the thread. #6-32 and #8-32 are used both on top of the playfield (holding plastics and ramps) and underneath (mechanisms). They are consumables: after four or five removals the nylon no longer grips. Replace them, they cost around twenty cents.
• KEPS nuts (with a captive external tooth washer) — common on board brackets and earth points.
• Serrated flange screws — the teeth under the head bite into the sheet metal.
• Spring / shakeproof washers — the period solution, still perfectly valid.
• Threadlocker — use low strength (blue) only, and never on plastic or on anything you will need to dismantle often. High strength (red) threadlocker has no place on a pinball machine.

Tightening torque: never force into 45-year-old plywood

A pinball playfield is plywood, often 1/2" (12.7 mm), covered with screen-printed artwork and clear coat. After 40 or 50 years that wood has been through humidity, temperature cycling and sometimes dozens of strip-downs. The fibres around the screw holes are tired.

Survival rules:

• Tighten by hand, never with a power driver on the playfield. A power driver strips a #6 hole in a fraction of a second. If you must use one, set the clutch to the absolute minimum and finish by hand.
• Stop as soon as the head touches down. A further quarter turn makes nothing stronger, it just crushes the fibres.
• Never drive a wood screw "dry" into a stubborn hole. A touch of candle wax or dry soap on the thread halves the torque required.
• On posts, over-tightening cracks the clear coat around the base and shatters plastics.
• On machine screws into thin sheet brackets, over-tightening bends the bracket and puts the mechanism out of adjustment (typically flipper brackets and drop targets).

These precautions are part of the routine described in our pinball cleaning and maintenance guide.

How to identify an unknown screw

You have a screw in your hand and no idea what it is. Four-step method:

1. Measure the outside diameter with vernier callipers, across the thread crests. Compare with the table above: 2.8 mm → #4 · 3.5 mm → #6 · 4.2 mm → #8 · 4.8 mm → #10 · 9.5 mm → 3/8". If you land exactly on 3.0 / 4.0 / 5.0 mm, it is probably a metric replacement fitted by a previous owner — and therefore not the original screw.
2. Count the threads across one inch (25.4 mm). Lay a rule along the screw, align zero with a thread crest and count the crests over 25.4 mm. 32 → 32 TPI · 40 → 40 TPI · 16 → 16 TPI. Tip: count over 1/2" (12.7 mm) and double it, which is easier on short screws.
3. Use a thread pitch gauge. A combined imperial/metric gauge costs about ten euros and settles any doubt in three seconds. It is the best value tool in the pinball workshop.
4. Test on a known nut. Keep a #6-32, a #8-32 and an M4 nut on the bench. The right screw runs through the full depth of the nut with no effort.

Measuring length: under the head for a pan, round or hex head; overall length (including the head) for a countersunk head.

Repairing a stripped screw hole in the playfield

The hole spins freely and the screw no longer holds? This is the most common problem on a playfield that has been stripped down many times. Three solutions, from lightest to strongest:

1. Toothpicks or bamboo + wood glue (the classic)

Push two or three round wooden toothpicks (harder than square ones) coated with wood glue (Titebond type) into the hole, snap them off flush, let it cure for at least 2 hours — ideally overnight — then drive the screw back in. Do not pre-drill: the wood screw cuts its own path. Effective for a #6, often enough for a #8. Bamboo skewers are harder still and hold better in badly ovalised holes.

2. Wooden dowel

For a genuinely destroyed hole: drill cleanly to 6 mm (1/4") or 8 mm (5/16"), glue in a dowel of the same diameter, trim flush, let it cure for 24 hours, then drill a fresh pilot hole at the screw core diameter (roughly 2.4 mm for a #6, 2.9 mm for a #8) before driving the screw. This is the permanent repair.

3. Through-fitted T-nut

When the hole is beyond saving and the area allows it, drill right through and fit a #6-32 or #8-32 T-nut under the playfield. You then move from a wood screw to a machine screw — a solution the manufacturers themselves used at certain heavily loaded locations. Take care not to drill where a mechanism or an insert sits.

Never do this: fitting a bigger screw (#8 in place of a #6) to "take up the slack". You gain one reassembly and you condemn the hole for good. Do not put cyanoacrylate glue alone into a hole either: it makes the wood brittle and rules out a clean repair afterwards. This section complements our vintage pinball restoration guide.

Where to buy pinball fasteners in Europe

The good news: pinball hardware is cheap and assortment kits exist. The less good news: you have to order from a specialist.

• PU-parts.com (Pinball Universe, Germany) — a very well stocked "Screws & Nuts" category, filterable by size #4 / #6 / #8 / #10 / 3/8". Intra-EU shipping, no customs. The easiest option from mainland Europe.
• Pinballshop.nl (Netherlands) — very large stock of Bally, Williams, Stern and Gottlieb parts.
• Pinball.center (Pinballcenter GmbH, Germany) — another major European distributor.
• Ministry of Pinball (Netherlands) — parts and mods.
• Pinball Heaven (United Kingdom) — mind the customs charges since Brexit if you order from the EU.
• Marco Specialties and Pinball Life (United States) — the most complete catalogue in the world, with original part numbers. Shipping from the USA: budget for carriage and import VAT. Worth it mainly for large orders or parts unobtainable in Europe.
• Industrial fastener suppliers — for standard machine screws (#6-32, #8-32, 3/8"-16), any UNC/UNF fastener supplier will do and costs less. For post studs and pinball-specific lengths, however, you need a specialist.

Tip: buy an assortment ("hardware kit") at the start of a restoration. A #6/#8 assortment in several lengths costs less than three successive orders of postage.

Points we could not verify with certainty

In the interests of honesty: several restorer discussions on Pinside report that certain post stud lengths — notably the #6 x 1-5/8" (41.3 mm) and the #6 x 1-3/4" (44.5 mm) — have become hard to find or are no longer manufactured. We were unable to confirm this with a manufacturer source. Check availability with your supplier before planning a full reassembly, and have a neighbouring length as a fallback. Likewise, the spanner sizes quoted for nuts (5/16", 11/32", 3/8") are the standard ANSI dimensions; some machines use non-standard nuts.

FAQ — pinball screws

Are pinball screws metric or imperial?

Imperial, always, on every American machine (Gottlieb, Bally, Williams, Data East, Sega, Stern) from 1930 to today. The standards used are UNC and UNF. No metric screw is interchangeable with an imperial screw of similar diameter.

Can an M4 screw replace a #8-32?

No. The diameter is close (4.00 mm against 4.17 mm) but the pitch differs (0.700 mm against 0.794 mm). The M4 engages two or three turns then jams; forcing it destroys the female thread. Never do it.

What are the two most common screw sizes on a pinball machine?

The #6-32 (Ø 3.51 mm) and #8-32 (Ø 4.17 mm) machine screws. Together with the matching #6 and #8 wood screws, these four references cover most of a machine.

Which screw holds a playfield post?

The standard is a #8 x 1-1/16" post stud (Ø 4.17 mm, length 27.0 mm) with a 6-32 machine thread on top. Short posts use #6 x 1-1/2" (38.1 mm) or 1-5/8" (41.3 mm), and tall posts generally #6 x 1-3/4" (44.5 mm).

What size are pinball leg bolts?

3/8"-16 x 2-1/2", that is a diameter of 9.525 mm, a pitch of 1.588 mm and a length of 63.5 mm, with a 5/8" (15.9 mm) acorn head. An extended 2-3/4" (69.9 mm) version exists to make room for cabinet protectors. Leg levellers use the same 3/8"-16 thread, with a 2" (50.8 mm) or 3" (76.2 mm) stem.

Which screwdriver do I need for a pinball machine?

A Phillips PH1 for #4 and #6 screws, a Phillips PH2 for #8 and #10, a parallel-sided flat blade for older machines, plus 1/4" (6.35 mm), 5/16" (7.94 mm), 11/32" (8.73 mm) and 5/8" (15.9 mm) sockets for hex heads and nuts.

How do I repair a screw hole that spins freely in the playfield?

Push in round toothpicks or bamboo splinters coated with wood glue, snap them off flush, leave overnight and drive the screw back in. For a badly damaged hole, drill to 6 or 8 mm, glue in a wooden dowel, leave 24 hours, drill a fresh pilot hole and refit. As a last resort, fit a through T-nut and switch to a machine screw.

Why does a pinball machine use nyloc nuts?

Because a pinball machine vibrates constantly. Without a locking feature the nuts work loose within a few hundred games. #6-32 and #8-32 nyloc nuts are consumables: after four or five removals the nylon ring no longer grips and they need replacing.

Sources & further reading

• Marco Specialties — Machine Screws (reference catalogue with original part numbers)
• Pinball Life — Hardware
• Titan Pinball — Pinball Hardware
• PinWiki — Pinball Leg Guide (leg bolts and levellers)
• Pinside — Standard size hardware across games
• Pinside — How to repair a screw hole
• PU-parts.com — Screws & Nuts (European supplier)
• The Pinball Resource — Post Screws

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