---
title: "What Are R-Clips (Hairpin Cotter Pins) Used For?"
description: "R-Clips (Hairpin Cotter Pins) (Trade series (hairpin cotter)) are used for connections made and broken by hand many times, where a threaded fastener would be…"
url: https://engineeringhardware.com/applications/r-clips-hairpin-cotters/
source: Engineering Hardware & Fasteners
---

# What Are R-Clips (Hairpin Cotter Pins) Used For?

Pins · Trade series (hairpin cotter) · Application guide

Typical applications, the industries that specify r-clips (hairpin cotter pins), and how to choose the right size, material and finish for the joint.

R-Clips (Hairpin Cotter Pins) are used for connections made and broken by hand many times, where a threaded fastener would be far too slow. They are manufactured to Trade series (hairpin cotter), and selection is driven by the nominal diameter, the fit and tolerance the assembly requires, and the service environment.

- **Primary duty:** Connections made and broken by hand many times, where a threaded fastener would be far too slow
- **Governing standard:** Trade series (hairpin cotter)
- **Nominal diameter range:** 5 mm to 16 mm
- **Category:** Pins

Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation.

![What Are R-Clips (Hairpin Cotter Pins) Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/09/R-Clips-Hairpin.webp)

The primary duty of R-Clips (Hairpin Cotter Pins) is connections made and broken by hand many times, where a threaded fastener would be far too slow. Below: the sectors that specify them in volume, the checklist used to select the right size and material for the application, installation notes, and the known limits of the type. Stocked across roughly 5 mm to 16 mm, they cover general to heavy-duty work.

## Typical Applications for R-Clips (Hairpin Cotter Pins)

The most common settings where these are specified:

- **Fabrication & metalwork:** bench and on-site assembly of steel frames, enclosures and weldments.
- **Jigs & fixtures:** precise location of tooling plates and locating features.
- **Linkages & hinges:** pivot points carrying light shear.
- **Machine alignment:** dowelling mating housings so they reassemble in the same position.
- **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment.

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## How to Specify R-Clips (Hairpin Cotter Pins) for Your Application

- **Size:** Select on nominal diameter, then on the hole tolerance and fit class — the fit, not the diameter alone, determines whether the part locates or slips. This product spans 5 mm–16 mm; check the full table below for the exact dimensions of each size.
- **Material:** Choose the material and finish for the service environment — plated steel for general use, stainless for corrosion resistance.
- **Environment:** For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient.
- **Standard:** This product is supplied to Trade series (hairpin cotter). Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

## Installation & Assembly Practice

- Ream the hole to the specified fit class; a dowel pressed into a drilled-only hole will not locate accurately.
- Press pins in with steady force rather than hammer blows where possible, and chamfer the hole entry.

## Common Selection Mistakes with R-Clips (Hairpin Cotter Pins)

- Using a dowel pin as a load-carrying shear bolt — dowels locate, they are not sized for sustained shear.
- Ignoring the fit class: a locational fit and an interference fit need different hole tolerances.

## Where R-Clips (Hairpin Cotter Pins) Are Not the Right Choice

Not for carrying significant tensile or repeated heavy shear loads — use a bolt or a keyed joint for that.

Custom manufacturing · Made to drawing

## Need a r-clips (hairpin cotter pins) outside the standard range?

End form, hardness and surface finish are all variable; the diameter tolerance is the one that decides the process. Made by cold heading or turning.

Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

[Custom pin manufacturing](https://engineeringhardware.com/custom/pins/)[Send a drawing](https://engineeringhardware.com/custom/pins/#rfq)

## Technical Drawing

Dimensioned line drawing of 5 R-Clips (Hairpin Cotter Pins) to Trade series (hairpin cotter). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Wire diameter (mm):** 1.6
- **Usable length (mm):** 30
- **Overall length (mm):** 40
- **Fits cross hole (mm):** 2.0
- **Material:** Spring steel
- **Finish:** Zinc plated
- **Re-use:** Yes, if not sprung

## Dimensions & Specifications (Trade series (hairpin cotter))

| For pin diameter (mm) | Wire diameter (mm) | Usable length (mm) | Overall length (mm) | Fits cross hole (mm) | Material | Finish | Re-use |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 5 | 1.6 | 30 | 40 | 2.0 | Spring steel | Zinc plated | Yes, if not sprung |
| 6 | 2.0 | 40 | 52 | 2.5 | Spring steel | Zinc plated | Yes, if not sprung |
| 8 | 2.5 | 50 | 65 | 3.0 | Spring steel | Zinc plated | Yes, if not sprung |
| 10 | 3.0 | 60 | 80 | 3.5 | Spring steel | Zinc plated | Yes, if not sprung |
| 13 | 4.0 | 80 | 105 | 4.5 | Spring steel | Zinc plated | Yes, if not sprung |
| 16 | 5.0 | 100 | 130 | 5.5 | Spring steel | Zinc plated | Yes, if not sprung |

Inside the plant

## Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift.
2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g.
3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1.
4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227.

## Frequently Asked Questions

### How do I choose the right size of R-Clips (Hairpin Cotter Pins)?

Select on nominal diameter and on the fit the assembly requires. This product is available from 5 mm to 16 mm; the full dimension table on this page lists each size.

### What material should R-Clips (Hairpin Cotter Pins) be for outdoor use?

For damp, coastal or chemical environments specify A4 (316) stainless or a suitably coated steel. For indoor or dry use, A2 (304) stainless or zinc-plated steel is normally adequate.

### Are R-Clips (Hairpin Cotter Pins) made to a recognized standard?

Yes — they are manufactured to Trade series (hairpin cotter), so dimensions are interchangeable between suppliers when you quote the standard on your order.

### What are R-Clips (Hairpin Cotter Pins) used for?

Connections made and broken by hand many times, where a threaded fastener would be far too slow. They are supplied to Trade series (hairpin cotter).

### Can I get a quote for R-Clips (Hairpin Cotter Pins) in the size and material I need?

Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time.

## Related Pages

Product page: [R-Clips (Hairpin Cotter Pins) — specifications & sizes](https://engineeringhardware.com/fastener/r-clips-hairpin-cotters/)

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