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Coiled Spring Pin Size Chart (ISO 8748 Heavy Duty)

Guide · Updated October 28, 2026

A coiled spring pin, also called a spiral pin, is a strip of spring steel wound about 2¼ turns into a solid-looking cylinder. Like a slotted roll pin, it is a little bigger than its hole and holds by spring pressure. Unlike a slotted pin, there is no gap, so the load is spread evenly around the bore and the pin flexes as one piece under shock. ISO 8748 covers the heavy-duty coiled pin from 1.5 mm to 20 mm. The nominal size is the hole size. The figures below come from the ISO 8748:2007 preview table and match Ferrobolt’s ISO 8748 dimensional chart.

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Step by step

Pick the nominal size: Pick the nominal diameter from the shear load and the room you have. As with roll pins, the nominal size is the hole you drill, not the pin.
Drill the hole to nominal: Drill the hole to the nominal size. ISO 8748 calls for an H12 hole for 1.5 mm and up, so a sharp jobber drill in a rigid setup is normally good enough.
Check the pin before fitting: Mike the pin across the coil. It should read inside the before-fitting d1 range in the chart, a few hundredths to a few tenths of a millimetre over the hole.
Choose the material column: Use the steel / martensitic stainless shear column for carbon or 420-type pins, and the lower austenitic column for 302/304-type stainless pins.
Drive from the chamfered end: Start the swaged chamfer in the hole and drive with a pilot-nose roll pin punch or press it in. A press gives the most even entry in long pins.
Ignore orientation: Coiled pins have no slot, so there is no need to orient them to the load. The 2¼ coils share the stress all the way around.

ISO 8748 heavy-duty coiled pin dimensions (mm)

Columns are: nominal size (the hole), diameter d1 before fitting (min–max), chamfer diameter d2 max before fitting, chamfer length a (approximate), strip wall thickness s, and minimum double shear load in kN. The first shear column applies to steel and martensitic stainless pins; the second applies to austenitic stainless pins.

Nominal (hole) | d1 before fitting (min–max) | d2 max | a ≈ | Wall s | Double shear kN steel | Double shear kN austenitic
1.5 | 1.61–1.71 | 1.4 | 0.5 | 0.17 | 1.9 | 1.45
2 | 2.11–2.21 | 1.9 | 0.7 | 0.22 | 3.5 | 2.5
2.5 | 2.62–2.73 | 2.4 | 0.7 | 0.28 | 5.5 | 3.8
3 | 3.12–3.25 | 2.9 | 0.9 | 0.33 | 7.6 | 5.7
3.5 | 3.64–3.79 | 3.4 | 1 | 0.39 | 10 | 7.6
4 | 4.15–4.30 | 3.9 | 1.1 | 0.45 | 13.5 | 10
5 | 5.15–5.35 | 4.85 | 1.3 | 0.56 | 20 | 15.5
6 | 6.18–6.40 | 5.85 | 1.5 | 0.67 | 30 | 23
8 | 8.25–8.55 | 7.8 | 2 | 0.9 | 53 | 41
10 | 10.30–10.65 | 9.75 | 2.5 | 1.1 | 84 | 64
12 | 12.35–12.75 | 11.7 | 3 | 1.3 | 120 | 91
14 | 14.40–14.85 | 13.6 | 3.5 | 1.6 | 165 | —
16 | 16.40–16.90 | 15.6 | 4 | 1.8 | 210 | —
20 | 20.40–21.00 | 19.6 | 4.5 | 2.2 | 340 | —

Standard lengths run from 4 mm to 200 mm (nominal 4, 5, 6, 8, 10, 12 … 100, 120, 140, 160, 180, 200), and ISO 8748 adds 20 mm steps above that. Length tolerance is ±0.25 mm up to 10 mm long, ±0.5 mm from 12 to 50 mm, and ±0.75 mm from 55 mm up. Not every length is made in every diameter, so check the commercial range on your supplier’s sheet.

Worked example: sizing a coiled pin for a drive collar

A collar on a 30 mm shaft carries 220 N·m. A cross pin through collar and shaft runs in double shear. The force at the pin is the torque divided by the shaft radius: 220 / 0.015 ≈ 14,700 N, or 14.7 kN. An 8 mm heavy-duty coiled pin in steel is rated 53 kN double shear, which gives a safety factor of about 3.6. A 6 mm pin (30 kN) would give about 2.0. With shock loading or reversing torque, the 8 mm pin is the better pick.

Now say the part is a food-machine shaft and the pin has to be 304 stainless. Use the austenitic column: 8 mm drops to 41 kN, so the safety factor becomes 41 / 14.7 ≈ 2.8. That is still acceptable for most steady loads. Check that the hole doesn’t weaken the shaft too much: an 8 mm cross hole in a 30 mm shaft removes about a quarter of the diameter, which is about the practical upper limit.

Worked example: checking a pin with a micrometer

A bin is labelled 5 × 24 ISO 8748. The chart says d1 before fitting should read 5.15 to 5.35 mm. Mike the pin across the coil at the middle (not on the chamfer). A reading of 5.22 mm is in range. A reading of 5.05 mm means the pin is probably a light-duty or standard-duty pin mixed into the bin, or one that has been driven out and lost its spring. Wall thickness tells them apart quickly: heavy duty is 0.56 mm at 5 mm, which you can see on the end with a loupe and a scale.

Heavy, standard and light duty

ISO 8748 heavy duty uses the thickest strip and gives the most shear. ISO 8750 standard duty is the general-purpose grade and is the most common coiled pin in stock. ISO 8751 light duty uses a thin strip for soft hosts such as aluminum, brass or plastic, where a heavy pin could crack the part or bulge a thin wall. Pick the lightest duty that carries the load: a lighter pin needs less force to drive and puts less stress on the hole. ASME B18.8.2 covers inch coiled pins, and its hole sizes are inch fractions, so never mix inch and metric charts.

Coiled vs slotted spring pins

Slotted roll pins (ISO 8752 heavy, ISO 13337 light) are cheaper and easy to find. Their shear rating at the same diameter is close to a heavy coiled pin, but they load the hole unevenly at the slot, and in vibration they can work loose or crack at the slot edge. Coiled pins have no orientation, spread stress around the full bore and have better fatigue life, so they are the usual choice for hinges, gear hubs and anything that sees cycling load.

Common problems

Pin walks out: the hole is oversize or bell-mouthed. Check it with a pin gage; if it takes a go pin at nominal + 0.1 mm or more, drill the next size up.
Pin collapses or telescopes when driving: the hole is too small or the parts are out of line. Use a pilot pin through the stack and support the far side.
Host cracks near the hole: move to a lighter duty, keep at least one diameter of edge distance, and chamfer the hole entry.
End mushrooms: use a pilot-nose punch, not a flat drift, and stop once the pin is flush.

FAQ

Is a coiled pin size the pin or the hole?

It is the hole. A 6 mm ISO 8748 coiled pin goes in a 6 mm hole and measures 6.18 to 6.40 mm before you drive it.

What is the difference between ISO 8748, 8750 and 8751?

They are the heavy, standard and light duty coiled pin standards. Heavy duty has the thickest strip and the highest shear rating; light duty suits soft or thin host material.

Is a coiled pin stronger than a slotted roll pin?

Not always in raw shear. A 6 mm ISO 8752 slotted pin is rated 26.04 kN versus 30 kN for an ISO 8748 coiled pin, so they are close. The coiled pin wins on fatigue and on even hole stress.

Why is there no austenitic value above 12 mm?

ISO 8748 only lists austenitic stainless shear values up to 12 mm. For 14, 16 and 20 mm the standard gives steel and martensitic stainless values only.

Pin and retaining-ring size charts

Picking a fastener to locate or retain a part? Compare the other pin and ring charts in this set:

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