---
title: "What Are Cap (Acorn) Nuts Used For?"
description: "Cap (Acorn) Nuts (DIN 1587) are used for exposed, hand-contact or decorative joints where the protruding thread must be covered. Catalogued M4 to M20."
url: https://engineeringhardware.com/applications/cap-acorn-nuts/
source: Engineering Hardware & Fasteners
---

# What Are Cap (Acorn) Nuts Used For?

Nuts · DIN 1587 · Application guide

Typical applications, the industries that specify cap (acorn) nuts, and how to choose the right size, material and finish for the joint.

Cap (Acorn) Nuts are used for exposed, hand-contact or decorative joints where the protruding thread must be covered. They are manufactured to DIN 1587, and the choice of size, property class and finish is driven by the load in the joint and the environment it sits in.

- **Primary duty:** Exposed, hand-contact or decorative joints where the protruding thread must be covered
- **Governing standard:** DIN 1587
- **Thread size range:** M4 to M20
- **Category:** Nuts

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

![What Are Cap (Acorn) Nuts Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/06/Cap-Acorn-Nuts-—-DIN-1587.webp)

Cap (Acorn) Nuts (DIN 1587) are specified where the joint requires exposed, hand-contact or decorative joints where the protruding thread must be covered. The sections below cover the typical end-uses by industry, the size and material decisions for each, assembly practice, and the applications this fastener type is not suited to. Stocked across roughly M4 to M20, they cover general to heavy-duty work.

## Typical Applications for Cap (Acorn) Nuts

The most common settings where these are specified:

- **Bolted joints:** the clamping counter-face on studs and bolts across every assembly type.
- **Vibration-prone equipment:** where a locking or flanged style resists loosening.
- **Frames & weldments:** captive or welded options for repeatable assembly.
- **Exposed assemblies:** handrails, furniture and equipment people touch.
- **Sanitary & decorative:** covering the thread end for a clean, safe finish.

## How to Specify Cap (Acorn) Nuts for Your Application

- **Size:** Match the nominal size to the mating thread or hole. This product spans M4–M20; check the full table below for the exact dimensions of each size.
- **Locking & grade:** Match the strength grade to the bolt, and choose a locking style (nyloc, all-metal, serrated flange) if the joint sees vibration.
- **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 DIN 1587. Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

## Installation & Assembly Practice

- Run the nut down by hand before applying the wrench to catch cross-threading early.
- Tighten the nut rather than the bolt head where access allows — the torque-to-preload relation is more consistent.
- For locking styles, note that nyloc inserts are single-use in critical joints and lose grip above roughly 120 °C.

## Common Selection Mistakes with Cap (Acorn) Nuts

- Pairing a high-class bolt with a lower-class nut — the nut strips before the bolt reaches proof load; the nut class must meet or exceed the bolt class.
- Using a plain nut with a spring washer in severe vibration instead of a prevailing-torque locking nut.
- Re-using nyloc nuts in critical joints.

## Where Cap (Acorn) Nuts Are Not the Right Choice

Not on their own — they need a matching bolt or stud — and a plain nut is not a substitute for a locking type under heavy vibration.

Custom manufacturing · Made to drawing

## Need a cap (acorn) nuts outside the standard range?

Height and across-flats are the two most often changed — a thinner nut for clearance, a larger hex for a tool that is already on the line. Made by cold heading or tapping.

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

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

## Technical Drawing

Dimensioned line drawing of M4 Cap (Acorn) Nuts to DIN 1587. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Pitch (mm):** 0.7
- **Width across flats s (mm):** 7.0
- **Width across corners e min (mm):** 7.66
- **Total height m (mm):** 8.0
- **Dome diameter (mm):** 7.0
- **Notes:** Closed-end domed cap nut, decorative / protective

## Dimensions & Specifications (DIN 1587)

| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Total height m (mm) | Dome diameter (mm) | Reference standard | Notes |
| --- | --- | --- | --- | --- | --- | --- | --- |
| M4 | 0.7 | 7.0 | 7.66 | 8.0 | 7.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M5 | 0.8 | 8.0 | 8.79 | 10.0 | 8.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M6 | 1.0 | 10.0 | 11.05 | 12.0 | 10.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M8 | 1.25 | 13.0 | 14.38 | 15.0 | 13.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M10 | 1.5 | 17.0 | 18.90 | 18.0 | 17.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M12 | 1.75 | 19.0 | 21.10 | 22.0 | 19.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M16 | 2.0 | 24.0 | 26.75 | 28.0 | 24.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |
| M20 | 2.5 | 30.0 | 33.53 | 34.0 | 30.0 | DIN 1587 | Closed-end domed cap nut, decorative / protective |

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

### Are Cap (Acorn) Nuts made to a recognized standard?

Yes — they are manufactured to DIN 1587, so dimensions are interchangeable between suppliers when you quote the standard on your order.

### What are Cap (Acorn) Nuts used for?

Exposed, hand-contact or decorative joints where the protruding thread must be covered. They are supplied to DIN 1587.

### Which industries use Cap (Acorn) Nuts?

They are commonly specified in frames & weldments, exposed assemblies and sanitary & decorative, among other sectors.

### How do I choose the right size of Cap (Acorn) Nuts?

Match the nominal size to the mating thread or hole. This product is available from M4 to M20; the full dimension table on this page lists each size.

### Can I get a quote for Cap (Acorn) Nuts 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: [Cap (Acorn) Nuts — specifications & sizes](https://engineeringhardware.com/fastener/cap-acorn-nuts/)

### Cap (Acorn) Nuts Specification Guides

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