Pinball Machine Screws: Every Size Explained (Inches and mm)

Looking for which screw to put back on 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 beware: all of these screws are imperial (inches), not metric. This guide gives every dimension in both systems, zone by zone, with conversion tables, head types, the right screwdrivers to use, and what to do when a playfield screw hole is stripped.

Why Pinball Machine Hardware Is Imperial

Pinball is an industry born in Chicago. Gottlieb, Williams, and Bally established their mechanical standards in the 1930s–1950s, long before Europe adopted the ISO metric system. Those standards never changed: a 2024 Stern pinball machine still uses #6-32 screws and 3/8"-16 leg bolts, exactly like a 1965 Gottlieb. This is great news for parts availability — pinball hardware is interchangeable across 70 years of production — but a permanent trap for the European restorer who has a box of metric screws at hand.

In practical terms: your local hardware store will not carry #6-32 screws. You need to order from a pinball parts supplier or a UNC/UNF fastener distributor. See the Where to Buy in Europe section below.

Understanding American Designations: What Does #6-32 x 1/2" Mean?

An American screw designation is read in three parts:

• The gauge number (#4, #6, #8, #10): this is the outside diameter of the threads. It is not a direct measurement but 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 inch fractions: 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, total length for a flat head. 1/2" = 12.7 mm.

A wood screw (sheet metal / wood screw) is noted differently: only the gauge and length, without TPI — "#8 x 1/2". The thread is self-tapping, with a very coarse pitch, designed to bite into the plywood playfield.

Complete Conversion Table: Inches ↔ Millimeters

The table below is the heart of this article. Keep it handy when you disassemble.

US Designation	Diameter (inches)	Diameter (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	The workhorse #1. Post tops, targets, plastics, coil brackets, ramps
#6 (wood screw)	0.138"	3.51 mm	self-tapping	—	Playfield underside (mechanisms, brackets, wire harnesses); short posts
#8-32	0.164"	4.17 mm	32 TPI	0.794 mm	The workhorse #2. Heavy mechanisms, flipper brackets, hinges, cabinet hardware
#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	Carriage bolts for the cabinet, heavy hinges
#10-32	0.190"	4.83 mm	32 TPI	0.794 mm	Backbox fasteners, locks, structural elements
3/8"-16	0.375"	9.525 mm	16 TPI	1.588 mm	Leg bolts and leg levelers. Universal on nearly all pinball machines

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 of this article. Here are the false friends:

• #8-32 vs M4: 4.17 mm vs 4.00 mm diameter, 0.794 mm vs 0.700 mm pitch. An M4 threads in two or three turns into a #8-32 tapped hole, then jams. Many restorers force it at that point — and strip the mechanism's threads. Not interchangeable.
• #6-32 vs M3.5: 3.51 mm vs 3.50 mm diameter — nearly identical! But the pitch is 0.794 mm vs 0.600 mm. This is the worst case: the screw engages confidently, then destroys everything. Not interchangeable.
• #4-40 vs M3: 2.84 mm vs 3.00 mm diameter. The M3 is too large — it simply will not go in.
• 3/8"-16 vs M10: 9.525 mm vs 10.00 mm diameter, 1.588 mm vs 1.500 mm pitch. An M10 leg bolt will not fit into a pinball machine leg plate. Do not improvise with the legs — they support 200 lbs of machine. On this topic, also read our pinball machine leg sizes guide.

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

Which Screw Goes Where: The Zone-by-Zone Table

Machine zone	Typical hardware	Dimensions (inches and mm)
Playfield top — wood rails, ball guides	Pan head wood screws, Phillips drive	#8 x 1/2" (4.17 mm dia., 12.7 mm length) — the most common; also #6 x 3/8" (3.51 mm dia., 9.5 mm)
Playfield posts (star posts, metal posts)	Combination stud screw: wood thread at the bottom, 6-32 machine thread at the top	#8 x 1-1/16" with 6-32 top (4.17 mm dia., 27.0 mm length)
Short posts	Post stud, wood thread	#6 x 1-1/2" (3.51 mm dia., 38.1 mm) or #6 x 1-5/8" (41.3 mm)
Tall posts	Long post stud	Typically #6 x 1-3/4" (3.51 mm dia., 44.5 mm)
Plastics, ramps, targets	Machine screws + nylon lock nuts	#6-32 x 3/8" to 1" (3.51 mm dia., 9.5 to 25.4 mm); #6-32 nylon lock nuts
Playfield underside — brackets, wire harnesses, microswitches	#6 wood screws, #6-32 and #4-40 machine screws	#6 x 3/8" and #6 x 1/2" (3.51 mm dia., 9.5 / 12.7 mm); #4-40 x 3/8" (2.84 mm dia., 9.5 mm)
Solenoids, flipper mechanisms	Machine screws + nylon lock nuts, often hex washer head	#8-32 (4.17 mm dia.) primarily, lengths 1/2" to 1-1/4" (12.7 to 31.8 mm)
Cabinet — hinges, brackets, lock, coin mechanism	#8 wood screws, #10-24 carriage bolts, #8-32 machine screws	#8 x 3/4" (4.17 mm dia., 19.1 mm); #10-24 x 1-1/4" (4.83 mm dia., 31.8 mm)
Backbox — circuit boards, hinges, lock	#6-32, #8-32, #10-32 machine screws; #8 wood screws	#6-32 x 1/2" (3.51 mm dia., 12.7 mm) for boards on standoffs
Legs	Acorn head leg bolts, adjustable levelers	3/8"-16 x 2-1/2" (9.525 mm dia., 63.5 mm length), 5/8" acorn head (15.9 mm). Extended version 2-3/4" (69.9 mm). Levelers: 3/8"-16 threaded rod, 2" (50.8 mm) or 3" (76.2 mm)

Note: these values are the most widespread standards (Williams, Bally, Stern, Gottlieb electronic machines). Some models, particularly Gottlieb electromechanical machines from the 1960s–70s and European manufacturers under license, deviate from these standards. Always verify on your machine before ordering in bulk.

Head Types and Where You Will Find Them

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

Drives and Screwdrivers: The Right Size Prevents 90% of the Damage

Cam-out that ruins a screw head almost always comes from an undersized screwdriver.

• Phillips (cross) — 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; a PH2 in a #6 will too. Keep both on hand.
• Slotted (flat blade) — on older and electromechanical machines. Use a parallel-sided blade (cabinet tip), not a tapered blade: the taper 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).
• Nut drivers — #6-32 nylon lock nuts are typically tightened with a 5/16" (7.94 mm) driver, #8-32 with 11/32" (8.73 mm), #10-32 with 3/8" (9.53 mm). A thin-wall socket wrench or ratchet is essential on the playfield.

A magnetic screwdriver and a magnetic parts tray will save you from the most tedious part of restoration: finding a screw that fell inside the cabinet. See our selection of essential tools for the pinball enthusiast.

Anti-Vibration and Nylon Lock Nuts: Why They Are Essential on a Pinball Machine

A pinball machine vibrates constantly: solenoids fire, pop bumpers strike, the ball hits at 3 m/s. Without locking, a machine screw loosens within a few hundred games. That is why virtually all machine-threaded hardware on a commercial pinball machine uses anti-loosening fasteners:

• Nylon lock nuts (nylon insert lock nuts) — a nylon ring inside the nut resists the threads. #6-32 and #8-32 sizes are used both on top of the playfield (securing plastics and ramps) and underneath (mechanisms). These are consumables: after 4–5 removals, the nylon no longer grips. Replace them — they cost about twenty cents each.
• KEPS nuts (captive star washer nuts) — common on board mounts and ground connections.
• Serrated flange screws — the teeth under the head bite into sheet metal.
• Split lock washers / star washers — the old-school solution, still perfectly effective.
• Threadlocker — use low-strength (blue) threadlocker only, and never on plastic or on a part you will need to disassemble frequently. High-strength (red) threadlocker has no place on a pinball machine.

Torque: Never Force Into 45-Year-Old Plywood

A pinball machine's playfield is plywood, typically 1/2" (12.7 mm), covered with silk-screened artwork and clear coat. After 40 or 50 years, that wood has endured moisture, temperature cycles, and sometimes dozens of disassemblies. The wood fibers around screw holes are fatigued.

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 use one, set the torque to the absolute minimum and finish by hand.
• Stop as soon as the head seats. A quarter turn more does not make anything stronger — it just crushes the wood fibers.
• Never drive a wood screw "dry" into a stubborn hole. A dab of candle wax or dry soap on the threads cuts the required torque in half.
• On posts, over-tightening cracks the clear coat around the base and shatters the plastics.
• On machine screws in thin sheet-metal brackets, over-tightening deforms the bracket and throws off the mechanism (typically flipper brackets and drop targets).

These precautions are part of the routine described in our pinball machine 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 calipers, on the thread crests. Compare to 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 screw installed by a previous owner — and therefore not the original.
2. Count the threads over one inch (25.4 mm). Place a ruler alongside the screw, align zero on a thread crest, and count how many crests span 25.4 mm. 32 → 32 TPI · 40 → 40 TPI · 16 → 16 TPI. Tip: count over 1/2" (12.7 mm) and double — easier on short screws.
3. Use a thread pitch gauge — a combined inch/metric gauge costs about ten dollars and removes all doubt in three seconds. It is the most cost-effective tool in the pinball workshop.
4. Test on a known nut. Keep a #6-32, a #8-32, and an M4 nut on the workbench. The correct screw threads smoothly through the full length of the nut.

Measuring length: under the head for pan, round, or hex heads; total length (including the head) for flat/countersunk heads.

Repairing a Stripped Screw Hole in the Playfield

The hole spins freely and the screw will not hold? This is the most common problem on a playfield that has been disassembled many times. Three solutions, from lightest to most solid:

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

Push two or three round wooden toothpicks (harder than square ones) coated with wood glue (such as Titebond) into the hole, snap them flush, and let it dry for at least 2 hours — ideally overnight — then re-drive the screw. Do not pre-drill: the wood screw will cut its own path. Effective for a #6, often sufficient for a #8. Bamboo skewers are even harder and hold better in badly ovalized holes.

2. Wooden dowel

For a badly damaged hole: drill cleanly at 6 mm (1/4") or 8 mm (5/16"), glue in a wooden dowel of the same diameter, trim flush, let dry 24 hours, then drill a pilot hole at the screw's core diameter (about 2.4 mm for a #6, 2.9 mm for a #8) before re-driving. This is the permanent repair.

3. T-nut (through-bolt)

When the hole is beyond saving and the location allows it, drill all the way through and install a #6-32 or #8-32 T-nut on the underside of the playfield. You then switch from a wood screw to a machine screw — a solution used by manufacturers at some high-stress locations from the factory. Be careful not to drill into a mechanism or insert on the other side.

Never do this: use a larger screw (#8 in place of a #6) to "make up the difference." You gain one reassembly and permanently ruin the hole. Also do not put cyanoacrylate (super glue) alone into a hole: it makes the wood brittle and makes a proper repair impossible later. This section complements our vintage pinball machine restoration guide.

Where to Buy Pinball Machine Hardware in Europe

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

• PU-parts.com (Pinball Universe, Germany) — well-stocked "Screws & Nuts" category, filterable by size #4 / #6 / #8 / #10 / 3/8". Ships within the EU, no customs. The simplest option from 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) — note the customs charges since Brexit.
• Marco Specialties and Pinball Life (United States) — the most complete catalog in the world, with original part numbers. Ships from the USA: factor in shipping costs and import VAT. Cost-effective mainly for large orders or parts unavailable in Europe.
• Industrial fastener suppliers — for standard machine screws (#6-32, #8-32, 3/8"-16), any UNC/UNF fastener supplier will work and costs less. However, for post studs and pinball-specific lengths, you need a specialist.

Tip: buy assortment kits ("hardware kits") at the start of a restoration. A #6/#8 assortment in multiple lengths costs less than three separate orders with shipping each time.

Points We Could Not Verify with Certainty

In the interest 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 difficult to find and may no longer be manufactured. We could not confirm this with a manufacturer source. Check availability with your supplier before planning a full reassembly, and plan for a neighboring length as a fallback. Similarly, the nut wrench sizes listed (5/16", 11/32", 3/8") are standard ANSI dimensions; some machines use non-standard nuts.

FAQ — Pinball Machine Screws

Are pinball machine screws metric or imperial?

Imperial, without exception, on all American machines (Gottlieb, Bally, Williams, Data East, Sega, Stern) from 1930 to the present day. The standards used are UNC and UNF. No metric screw is interchangeable with an imperial screw of a similar diameter.

Can an M4 screw replace a #8-32?

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

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

#6-32 (3.51 mm dia.) and #8-32 (4.17 mm dia.) machine screws. Together with #6 and #8 wood screws, these four references cover the bulk of any machine.

What screw holds a playfield post?

The standard is a #8 x 1-1/16" post stud (4.17 mm dia., 27.0 mm length) with a 6-32 machine thread at the top. For short posts you will find #6 x 1-1/2" (38.1 mm) or 1-5/8" (41.3 mm), and for tall posts typically #6 x 1-3/4" (44.5 mm).

What size are pinball machine leg bolts?

3/8"-16 x 2-1/2": 9.525 mm diameter, 1.588 mm pitch, 63.5 mm length, with a 5/8" (15.9 mm) acorn head. An extended 2-3/4" (69.9 mm) version exists for machines with cabinet protectors. Leg levelers use the same 3/8"-16 thread, with a 2" (50.8 mm) or 3" (76.2 mm) rod.

What 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 stripped screw hole in the playfield?

Push round toothpicks or bamboo splinters coated with wood glue into the hole, snap them flush, let dry overnight, and re-drive the screw. For a badly damaged hole, drill at 6 or 8 mm, glue in a wooden dowel, let dry 24 hours, drill a pilot hole, and re-drive. As a last resort, install a through T-nut and switch to a machine screw.

Why do pinball machines use nylon lock nuts?

Because a pinball machine vibrates constantly. Without locking, nuts loosen within a few hundred games. #6-32 and #8-32 nylon lock nuts are consumables: after four or five removals, the nylon ring no longer grips and they need to be replaced.

Sources & Further Reading

• Marco Specialties — Machine Screws (reference catalog with original part numbers)
• Pinball Life — Hardware
• Titan Pinball — Pinball Hardware
• PinWiki — Pinball Leg Guide (leg bolts and levelers)
• 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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