ASME B18.8.1 Cotter Pins (Inch Series)
ASME B18.8.1 cotter pins (split cotter pins), inch series 1/32 – 3/4 in — the two-prong wire retainer for clevis and slotted-nut assemblies, with the collected per-size table: basic pin diameter, total shank diameter, wire width, head diameter, extended prong length and gage hole diameter.
Last updated: 2026-11
Specifications
The ASME B18.8.1 cotter pin — the inch-series split cotter pin, folded from a half-round wire into two prongs — is the classic positive retainment of the inch world: it keeps a castle nut from backing off a shaft, holds a clevis pin in its eye, and is cheap enough to be the intended sacrificial part of the assembly. It is not a fastener you torque; it is one you install and then inspect, because its whole function lives in the prongs seating and spreading in the hole. The collected table runs 1/32 to 3/4 in nominal size and carries the dimensions that make the pin fit its mating parts: basic pin diameter, total shank diameter A (max/min — the source notes A is two times the wire thickness), wire width B, head diameter C (min), extended prong length D (min), and the gage hole diameter (±0.001) the pin must seat in — that gage column is the practical cross-check, since it is the hole the assembled prongs have to engage. Size ladder note: the source table starts at 1/32 in with the smallest wire sizes, jumps through the 1/4 – 3/4 range in the second block, and the two blocks are one continuous series — the mid-table header repeat is carried as a table footnote. Material and finish (carbon steel, stainless, silicon bronze are the class options) are not tabulated by the collected specification — per RFQ.
| Standard | ASME B18.8.1-1994 — clevis pins and cotter pins, inch series (cotter pin: two-prong wire retainer for slotted-nut and clevis assemblies) |
|---|---|
| Size range | Nominal 1/32 – 3/4 in, eighteen sizes (1/32, 3/64, 1/16 … 3/4); one geometry row per size |
| Tabulated geometry | Per size: basic pin dia., total shank dia. A (max/min; source note: A = two times wire thickness), wire width B (max/min), head dia. C (min), extended prong length D (min), gage hole dia. (+/- 0.001) |
| Gage hole column | The hole diameter the installed prongs must engage (0.047 – 0.750 across the range) — the practical fit check against the mating clevis or nut slot |
| Material / finish | Not tabulated by the collected specification — per RFQ (state material and finish at quotation) |
| Cotter Pin Size | Basic Pin Dia. | Total Shank Diameter (A) Max. | Total Shank Diameter (A) Min. | Wire Width (B) Max. | Wire Width (B) Min. | Head Diameter (C) Min. | Extended Prong Length (D) Min. | Gage Hole Diameter (+/- 0.001) |
|---|---|---|---|---|---|---|---|---|
| 1/32 | 0.031 | 0.032 | 0.028 | 0.032 | 0.022 | 0.06 | 0.01 | 0.047 |
| 3/64 | 0.047 | 0.048 | 0.044 | 0.048 | 0.035 | 0.09 | 0.02 | 0.062 |
| 1/16 | 0.062 | 0.060 | 0.056 | 0.060 | 0.044 | 0.12 | 0.03 | 0.078 |
| 5/64 | 0.078 | 0.076 | 0.072 | 0.076 | 0.057 | 0.16 | 0.04 | 0.094 |
| 3/32 | 0.094 | 0.090 | 0.086 | 0.090 | 0.069 | 0.19 | 0.04 | 0.109 |
| 7/64 | 0.109 | 0.104 | 0.100 | 0.104 | 0.080 | 0.22 | 0.05 | 0.125 |
| 1/8 | 0.125 | 0.120 | 0.116 | 0.120 | 0.093 | 0.25 | 0.06 | 0.141 |
| 9/64 | 0.141 | 0.134 | 0.130 | 0.134 | 0.104 | 0.28 | 0.06 | 0.156 |
| 5/32 | 0.156 | 0.150 | 0.146 | 0.150 | 0.116 | 0.31 | 0.07 | 0.172 |
| 3/16 | 0.188 | 0.176 | 0.172 | 0.176 | 0.137 | 0.38 | 0.09 | 0.203 |
| 7/32 | 0.219 | 0.207 | 0.202 | 0.207 | 0.161 | 0.44 | 0.10 | 0.234 |
| 1/4 | 0.250 | 0.225 | 0.220 | 0.225 | 0.176 | 0.50 | 0.11 | 0.266 |
| 5/16 | 0.312 | 0.280 | 0.275 | 0.280 | 0.220 | 0.62 | 0.14 | 0.312 |
| 3/8 | 0.375 | 0.335 | 0.329 | 0.335 | 0.263 | 0.75 | 0.16 | 0.375 |
| 7/16 | 0.438 | 0.406 | 0.400 | 0.406 | 0.320 | 0.88 | 0.20 | 0.438 |
| 1/2 | 0.500 | 0.473 | 0.467 | 0.473 | 0.373 | 1.00 | 0.23 | 0.500 |
| 5/8 | 0.625 | 0.598 | 0.590 | 0.598 | 0.472 | 1.25 | 0.30 | 0.625 |
| 3/4 | 0.750 | 0.723 | 0.715 | 0.723 | 0.572 | 1.50 | 0.36 | 0.750 |
- Row 1 (1/32): The printed sub-header row carries only six Max./Min. labels for the seven value columns (the gage-hole column is unlabeled in the source); per-column limits above follow the attribute list order.
- Row 12 (1/4): The source repeats the full column-header block mid-table (between the 7/32 and 1/4 rows); the duplicate header is not reproduced as data here.
| Nominal Size (Basic Pin Dia.) | Nominal Size (decimal) | Length Max (L max) | Length Nom. (L nom) | Length Min (L min) |
|---|---|---|---|---|
| 1/32 | 0.031 | 0.53 | 0.5 | 0.47 |
| 3/64 | 0.047 | 0.53 | 0.5 | 0.47 |
| 1/16 | 0.062 | 0.53 | 0.5 | 0.47 |
| 3/32 | 0.094 | 0.53 | 0.5 | 0.47 |
| 3/32 | 0.094 | 0.53 | 0.5 | 0.47 |
| 5/32 | 0.156 | 0.78 | 0.75 | 0.72 |
| 5/32 | 0.156 | 0.78 | 0.75 | 0.72 |
| 1/4 | 0.250 | 1.06 | 1 | 0.94 |
| 5/16 | 0.312 | 1.06 | 1 | 0.94 |
| 3/8 | 0.375 | 1.56 | 1.5 | 1.44 |
| 1/2 | 0.500 | 2.56 | 2.5 | 2.44 |
| 5/8 | 0.625 | 3.06 | 3 | 2.94 |
- Row 5 (3/32): Duplicate rows appear at 3/32 (two identical rows) and 5/32 (two) — reproduced verbatim.
- Row 1 (1/32): Sizes 1/8 and 3/16 are absent from the published ladder. Verify against the governing standard before quoting those sizes.
Materials
- Material and finish specified per RFQ — state the service environment (corrosion exposure, temperature) with the order
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASME B18.8.1 Cotter Pins (Inch Series)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantities and lead times for this family are confirmed at quotation — send your sizes, grades and quantities on the RFQ and the quote will carry a firm schedule. Sample availability is confirmed with the quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
What does the gage hole column on a cotter pin table actually tell me?
It is the dimension that connects the pin to the part you are retaining. A cotter pin works by passing through a cross-hole and having its two prongs spread and seat on the far side — so the hole diameter is not optional trivia, it is the fit the pin geometry was standardized around. The collected table prints that gage hole for every size to ±0.001 in (0.047 in for the 1/32 pin, up to 0.750 in for the 3/4 pin): drill or buy the cross-hole to that figure and the pin of the matching size will pass through with the right clearance and seat properly. Too small and the pin will not enter or the prongs bind before seating; too large and the prongs cannot bridge the hole, so the pin rocks and the retainment is loose. Two more practical reads from the same table: the total shank diameter A is stated as two times the wire thickness, so the pin's cross-section in the hole is predictable from the wire width column; and the extended prong length D is a minimum — enough prong to bend back and still engage, which matters when the assembly will be disassembled and re-pinned. Hole size, pin size and prong bend travel together; order pins by the nominal size whose gage column matches your hole, and state material and finish at RFQ.
What is the MOQ and lead time for this pin type?
Commercial terms for this family are confirmed at quotation — state sizes, tolerance class and quantities on the RFQ for a firm schedule. Common diameters in this pin type are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support