Buy Cotter Pins Online in Australia
Cotter Pin / Split Pin Sizes — ISO 1234 Quick Reference
Cotter pins (split pins) are specified by nominal diameter (matches the drilled hole) and length. Manufactured to AS/NZS 1444 / ISO 1234 — the diameter matches the hole; the actual wire diameter is ~0.05 mm undersize for insertion clearance. Available zinc-plated mild steel (general use) or 316 stainless (marine, food, corrosive environments).
| Nominal Ø | Recommended Hole Ø | Common Length Range | Typical Use |
|---|---|---|---|
| 1.6 mm | 1.7 mm | 10 - 32 mm | Light hardware, small linkage, hobby |
| 2.0 mm | 2.1 mm | 10 - 40 mm | Castle nut M8-M10, small assemblies |
| 2.5 mm | 2.6 mm | 16 - 50 mm | Castle nut M10-M12, trailer hardware |
| 3.2 mm | 3.4 mm | 18 - 63 mm | Castle nut M12-M14, trailer hubs |
| 4.0 mm | 4.2 mm | 20 - 80 mm | Castle nut M14-M16, agricultural linkage |
| 5.0 mm | 5.2 mm | 25 - 100 mm | Heavy machinery, large castle nuts |
| 6.3 mm | 6.6 mm | 32 - 125 mm | Truck axles, large castle nuts M20+ |
| 8.0 mm | 8.5 mm | 40 - 160 mm | Heavy plant, very large castle nuts |
Cotter pins are the standard retention method for clevis pins through their cross-hole. For complete selection criteria including material grades, installation technique and alternatives, see our split pin / cotter pin guide. For springpin / roll pin alternatives, see spring pins.
Cotter Pins & Split Pins — Fastener Retention
Cotter pins (also called split pins) are safety fastening devices that lock clevis pins, castle nuts, axle pins and shaft pins against vibration loosening or accidental withdrawal. AIMS Industrial supplies cotter pins in metric and imperial sizes — zinc-plated mild steel for general applications and 316 stainless steel for marine, food and corrosive environment use. Manufactured to AS/NZS 1444 / ISO 1234 dimensional standards.
For complete coverage of selection, sizing, installation technique and when to use cotter pins vs alternatives, see our split pin / cotter pin guide.
Cotter pins we stock
- Zinc-plated mild steel cotter pins — metric sizes from 1.6 mm to 8 mm diameter. The general-purpose cotter pin for agricultural equipment, machinery, automotive and general fastener retention. Zinc plating provides light corrosion resistance for indoor and protected outdoor use.
- 316 stainless steel cotter pins — for marine, food processing and corrosive chemical environments. 316 grade provides chloride and oxidation resistance where zinc-plated steel would rust or pit. Matching metric sizes.
- Imperial cotter pins — inch diameter cotter pins for American and older machinery still using AF/UNC fastener systems. Critical where metric cotter pins would not correctly fit the pin hole diameter.
- Assortment packs — the most commonly used metric sizes in a single storage box. Practical for maintenance workshops and service vehicles where a range of sizes must be accessible without multiple individual packs.
Selection & installation
- Correct diameter fit — the cotter pin diameter must provide a snug fit in the hole. A loose fit allows the pin to rattle under vibration, eventually wearing out the hole and allowing withdrawal. Standard fit is within ±0.1 mm of the pin hole diameter in the fastener or shaft.
- Installation technique — after insertion, both legs of the cotter pin must be spread (bent): one leg bent back flat, the other bent forward, to prevent withdrawal under vibration. Never reuse a cotter pin after removal — the leg metal is work-hardened and may fracture when re-bent.
- Single-use fastener — cotter pins are single-use. Always replace with a new cotter pin after disassembly. Used pins may fracture on re-bending or have reduced retention capability from metal fatigue.
Companion pin ranges at AIMS
Cotter pins are typically installed through a clevis pin in a clevis-bracket-pin assembly. For solid-shaft retention without a clevis, see spring (roll) pins — the related roll pin guide covers the trade-offs between cotter, clevis, roll and tapered pins. Other related pin types: taper pins, coupling pins and linchpins.
For the full fastener range, see fasteners — including hex head screws, machine screws and stainless fasteners.
Australian business, local supply
As a proudly Australian business since 1988, we stock locally and work with trusted Australian manufacturers and distributors to ensure fast, reliable supply. Need help buying the right cotter pin for your application? Call (02) 9773 0122, contact our team or request a quote.