Engineering Tools · Cotter Pin Reference
Cotter Pin Size Chart (Split Pin) — ISO 1234 / GB/T 91-2000 Nominal Sizes, Lengths and Hole Fit
ISO 1234:1997 / GB/T 91-2000 (cotter pins / split pins) · equivalent adoption · distilled from a licensed standard copy, provenance in References below
A cotter pin (split pin) is pushed through a hole and its two legs are opened to lock it in place. This page sets out the 16 nominal sizes of ISO 1234:1997 / GB/T 91-2000 Table 1 (0.6–20 mm), the 33 nominal lengths of Table 2 (4–280 mm) and the technical requirements of Table 3 in one place. Read two diameters apart first: the nominal size d is the hole diameter, while d max / d min are the measured diameters of the pin body with both legs together — they are not the same number. The last two columns give the bolt and clevis-pin (U-pin) diameter ranges the pin matches.
At a glance: the 3.2 mm row
Nominal size 3.2 mm: pin body 2.7–2.9 mm, leg-end offset 1.6–3.2 mm, eye height ≈ 6.4 mm, eye width 5.1–5.8 mm; matching bolt 11–14 mm and clevis pin 9–12 mm; commodity length range 14–63 mm, recommended hole tolerance H14. The full table covers 16 nominal sizes and 33 nominal lengths (4–280 mm).
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Full dimension matrix (Table 1, mm)
Column order follows the source table. Nominal size d = hole diameter (table note 1); d max / d min = measured diameter of the pin body with both legs together, always below the nominal size; a max / a min = leg-end offset; b = height of the eye (marked ≈ in the source table); c max / c min = width of the eye.
| Nominal size d | d max | d min | a max | a min | b | c max | c min |
|---|---|---|---|---|---|---|---|
| 0.6 | 0.5 | 0.4 | 1.6 | 0.8 | 2 | 1 | 0.9 |
| 0.8 | 0.7 | 0.6 | 1.6 | 0.8 | 2.4 | 1.4 | 1.2 |
| 1 | 0.9 | 0.8 | 1.6 | 0.8 | 3 | 1.8 | 1.6 |
| 1.2 | 1 | 0.9 | 2.5 | 1.25 | 3 | 2 | 1.7 |
| 1.6 | 1.4 | 1.3 | 2.5 | 1.25 | 3.2 | 2.8 | 2.4 |
| 2 | 1.8 | 1.7 | 2.5 | 1.25 | 4 | 3.6 | 3.2 |
| 2.5 | 2.3 | 2.1 | 2.5 | 1.25 | 5 | 4.6 | 4 |
| 3.2 | 2.9 | 2.7 | 3.2 | 1.6 | 6.4 | 5.8 | 5.1 |
| 4 | 3.7 | 3.5 | 4 | 2 | 8 | 7.4 | 6.5 |
| 5 | 4.6 | 4.4 | 4 | 2 | 10 | 9.2 | 8 |
| 6.3 | 5.9 | 5.7 | 4 | 2 | 12.6 | 11.8 | 10.3 |
| 8 | 7.5 | 7.3 | 4 | 2 | 16 | 15 | 13.1 |
| 10 | 9.5 | 9.3 | 6.3 | 3.15 | 20 | 19 | 16.6 |
| 13 | 12.4 | 12.1 | 6.3 | 3.15 | 26 | 24.8 | 21.7 |
| 16 | 15.4 | 15.1 | 6.3 | 3.15 | 32 | 30.8 | 27 |
| 20 | 19.3 | 19 | 6.3 | 3.15 | 40 | 38.5 | 33.8 |
Matching diameters: bolt and clevis pin (sub-table of Table 1)
Both columns are taken cell by cell from the matching-diameter row of the source table, with intervals shaped (lower, upper]: the lower bound is open and the upper bound is closed, exactly as the source prints them in its > and ≤ sub-columns — not rewritten here as closed intervals. Where the source prints a dash at one end, only the other end is shown (an upper bound only on the smallest size, a lower bound only on the largest); nothing is extrapolated.
| Nominal size d | Matching bolt diameter | Matching clevis-pin diameter |
|---|---|---|
| 0.6 | ≤2.5 | ≤2 |
| 0.8 | 2.5–3.5 | 2–3 |
| 1 | 3.5–4.5 | 3–4 |
| 1.2 | 4.5–5.5 | 4–5 |
| 1.6 | 5.5–7 | 5–6 |
| 2 | 7–9 | 6–8 |
| 2.5 | 9–11 | 8–9 |
| 3.2 | 11–14 | 9–12 |
| 4 | 14–20 | 12–17 |
| 5 | 20–27 | 17–23 |
| 6.3 | 27–39 | 23–29 |
| 8 | 39–56 | 29–44 |
| 10 | 56–80 | 44–69 |
| 13 | 80–120 | 69–110 |
| 16 | 120–170 | 110–160 |
| 20 | >170 | >160 |
Commodity length range and recommended hole tolerance
The commodity length range is the band framed by the bold boundary lines of Table 2 for that nominal size (mm): the lengths that size is made in. Order inside that band, and take the nominal length from Table 2. The recommended hole tolerance comes from table note 1: H13 for a nominal size of 1.2 mm or less, and H14 above it.
| Nominal size d | Commodity length range | Recommended hole tolerance |
|---|---|---|
| 0.6 | 4–12 | H13 |
| 0.8 | 5–16 | H13 |
| 1 | 6–20 | H13 |
| 1.2 | 8–25 | H13 |
| 1.6 | 8–32 | H14 |
| 2 | 10–40 | H14 |
| 2.5 | 12–50 | H14 |
| 3.2 | 14–63 | H14 |
| 4 | 18–80 | H14 |
| 5 | 22–100 | H14 |
| 6.3 | 32–125 | H14 |
| 8 | 40–160 | H14 |
| 10 | 45–200 | H14 |
| 13 | 71–250 | H14 |
| 16 | 112–280 | H14 |
| 20 | not marked in the source table | H14 |
Note: the source table gives no boundary line at all for the 20 mm nominal size, so it defines no commodity length range for that size. It is reported here as not marked, and no value is extrapolated.
Note: on the 16 mm nominal size the source table marks only the lower end of the range; the upper end falls beyond the last length step of Table 2 (280 mm). It is reported here as lower end to 280 mm.
Nominal lengths and limit lengths (Table 2, mm)
33 nominal lengths from 4 to 280 mm; min and max are the lower and upper limit lengths of each step. Both legs must pass through the hole and open on the far side, so measure the length you need at the joint: check the commodity length range above first, then inspect against the limits in this table.
| Nominal length l | l min | l max |
|---|---|---|
| 4 | 3.5 | 4.5 |
| 5 | 4.5 | 5.5 |
| 6 | 5.5 | 6.5 |
| 8 | 7.5 | 8.5 |
| 10 | 9.5 | 10.5 |
| 12 | 11 | 13 |
| 14 | 13 | 15 |
| 16 | 15 | 17 |
| 18 | 17 | 19 |
| 20 | 19 | 21 |
| 22 | 21 | 23 |
| 25 | 24 | 26 |
| 28 | 27 | 29 |
| 32 | 30.5 | 33.5 |
| 36 | 34.5 | 37.5 |
| 40 | 38.5 | 41.5 |
| 45 | 43.5 | 46.6 |
| 50 | 48.5 | 51.5 |
| 56 | 54.5 | 57.5 |
| 63 | 61.5 | 64.5 |
| 71 | 69.5 | 72.5 |
| 80 | 78.5 | 81.5 |
| 90 | 88 | 92 |
| 100 | 98 | 102 |
| 112 | 110 | 114 |
| 125 | 123 | 127 |
| 140 | 138 | 142 |
| 160 | 158 | 162 |
| 180 | 178 | 182 |
| 200 | 198 | 202 |
| 224 | 222 | 226 |
| 250 | 248 | 252 |
| 280 | 278 | 282 |
Technical requirements (Table 3 and its notes)
Row by row from GB/T 91-2000 Table 3 and its table notes: material, surface treatment, surface defects, work quality, mechanical properties, hole tolerance, agreed sizes, designation example, and the case where one size larger is recommended. Grades and referenced standards are as given by the standard and are not rewritten here.
| Item | Requirement |
|---|---|
| Material (referenced standard in brackets) | carbon steel Q215 / Q235 (GB/T 700); copper alloy H63 (GB/T 5232); stainless steel 1Cr17Ni7 / 0Cr18Ni9Ti (GB/T 1220) |
| Surface treatment (referenced standard in brackets) | as formed, no treatment; electroplated (GB/T 5267); phosphated (GB/T 11376) |
| Surface defects | Burns, irregular and harmful defects are not permitted. |
| Work quality | The eye should be as circular as possible and both legs should have a circular cross-section. The binding rule is this: the gap between the legs and the leg-end offset must not exceed the difference between the nominal size and d max — on the 3.2 mm row used as the example above, d max is 2.9 mm and gap plus offset together may not exceed that difference. |
| Mechanical properties (bend test) | Each leg must withstand reverse bending once — bent through 90° and back, 1 cycle — without breaking. The test is per the standard; this page is not a test report. |
| Hole tolerance | Hole tolerance H13 for a nominal size of 1.2 mm or less, and H14 above it (table note 1). The nominal hole diameter equals the nominal size d. |
| Agreed sizes | Nominal sizes that may be used by agreement between supplier and buyer (table note 1): 3.6 / 12 mm |
| Designation example | Designation example: Split pin GB/T 91 5×50 (nominal size 5 mm × length 50 mm). |
| When to go one size larger | For railway use, and in clevis pins carrying alternating lateral force, one size larger is recommended (table note 2). |
Basis & Disclosed Assumptions
Where the numbers come from
- Every dimension, length step and technical requirement is taken cell by cell from GB/T 91-2000 Tables 1, 2 and 3, mechanically generated from a distillation of a licensed standard copy and read back against these constants with zero diff. This page, the acceptance script and the PDF generator share one constant, so every figure can be recalculated.
- The nominal size is the hole diameter (table note 1); d max / d min are the measured limits of the pin body with both legs together, not the nominal size itself — the Table 3 rule that leg gap and offset must not exceed the difference between the nominal size and d max confirms that reading.
- a max / a min is the tolerance band on the leg-end offset (always 2:1 across the 16 sizes, the lower value being half the upper — a value given by the standard, not a geometric derivation); b is the height of the eye, marked ≈ in the source table.
- The two matching-diameter sub-columns are taken from that row of the source table, with intervals shaped (lower, upper]: an upper bound alone is shown as ≤ upper and a lower bound alone as > lower, exactly as this page renders them.
Scope & limits
- Equivalent adoption of ISO 1234:1997. Every figure on this page follows the printed values of GB/T 91-2000 and is not recalculated to the ISO edition.
- The source table leaves the commodity length range of the 20 mm nominal size unmarked. That is stated as it is, with no extrapolated value (third-party manuals render it as 160–280, which conflicts with this reading, and non-standard sources are not adopted here).
- On the 16 mm nominal size the upper end of the commodity length range falls beyond the last length step of Table 2 (280 mm); it is reported as lower end to the last step, without extending into steps the standard does not give.
- The recommended hole tolerance splits at 1.2 mm (H13 at or below it, H14 above), and there are 33 nominal lengths, each with its own limit lengths. This family has no mass table and no weight calculator entry.
References
- GB/T 91-2000 Split pins — Table 1 dimensions, Table 2 nominal lengths, Table 3 technical requirements (National Public Service Platform for Standards Information)
- ISO 1234:1997 Split pins (the international edition this standard adopts)
- GB/T 1800.2-2020 Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes: source of the hole tolerance codes
Cite this chart
YAXIIO. Cotter Pin Size Chart (Split Pin) — ISO 1234 / GB/T 91-2000 Nominal Sizes, Lengths and Hole Fit. https://www.yaxiio.com/en/tools/cotter-pin-chart (accessed 2026-10-29).
Free to cite and embed — attribution required: “YAXIIO” + a link to this page.
FAQ
How do I choose the nominal size d?
Choose it from the hole diameter, not from the bolt you are securing: the nominal size d is the hole diameter (table note 1), and the matching bolt diameter is given separately as a range in the matching-bolt column — 11–14 mm on the 3.2 mm row. So measure the hole first, or start from the bolt and look that column up. An undersized hole will not let the pin body open, and an oversized one leaves the legs loose.
How do I choose the length l?
The length must let both legs pass through the hole and still leave enough to open on the far side. Start from the commodity length range of that nominal size (14–63 mm on the 3.2 mm row), pick a step from the 33 nominal lengths in Table 2 (4–280 mm), then inspect against that step's l min and l max. Lengths outside the range are non-preferred and are made to drawing.
Cotter pin or spring pin — which one?
Both retain, but differently. A cotter pin locks by opening its two legs behind the hole, is normally not reused, and needs assembly room for the legs to splay. A spring pin locks by radial spring force once it is pressed in, can be removed and refitted many times, and carries a shear load quoted in its own standard. Choose a spring pin for location duties, frequent disassembly or alternating lateral force; choose a cotter pin for shaft-end retention, where the opened legs can be seen and the cost matters.
How do I choose the material and surface treatment?
The standard lists three material groups (carbon steel, copper alloy and stainless steel) and three surface treatments (as formed, electroplated and phosphated); grades and referenced standards are in the technical table above. Avoid zinc-plated steel pins outdoors, in damp service or in contact with stainless parts; copper alloy suits non-magnetic or conductive duties; use a stainless pin in a stainless hole to avoid galvanic corrosion between dissimilar metals.
What are the hard requirements on the bend test and the hole?
Mechanical properties: each leg must withstand reverse bending once — 90° and back, 1 cycle — without breaking. That is an acceptance test, not the angle you open the legs to in service. Hole: H13 for a nominal size of 1.2 mm or less, and H14 above it (table note 1). One more work-quality rule applies: leg gap plus leg-end offset must not exceed the difference between the nominal size and d max.
The other family in this group: spring pins
Cotter pins and spring pins both retain inside a hole, but assembly, reusability and load data differ completely: a cotter pin is threaded through the hole and its legs are opened, while a spring pin locks by radial spring force as it is pressed in and carries a shear load quoted by its own standard. The two families often appear on the same drawing, so do not mix them up.
Open the spring pin size chart →Related References
Bolt Size Chart
GB/T 5783 fully threaded and GB/T 5782 partially threaded hex bolts: width across flats, head height and head diameter, to read against the matching-bolt column above.
Wrench & Socket Size Chart
Look up the wrench and socket opening for a given width across flats before tightening the joint.
Tap Drill & Thread Engagement Chart
Metric coarse, metric fine and inch tap drill sizes: the other hole-making convention next to the cotter pin hole.
Spring Pin Size Chart
Slotted and coiled spring pins with their size matrices, length series and minimum double shear load (the other family in this group, for selection side by side).
Disclaimer: this chart provides engineering reference data for selection and quotation only; it is not a design basis or an acceptance standard.