---
title: "A4 (316) Stainless Steel EPDM Rubber Well Nuts"
description: "A4 (316) Stainless Steel EPDM Rubber Well Nuts (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80): superior, including marine and chloride"
url: https://engineeringhardware.com/guide/material/a4-stainless-steel-epdm-rubber-well-nuts/
source: Engineering Hardware & Fasteners
---

# A4 (316) Stainless Steel EPDM Rubber Well Nuts

Nuts · Trade series (rubber blind nuts)

Mechanical properties, corrosion behaviour and the full dimensional range for this grade.

A4 Stainless Steel EPDM Rubber Well Nuts are supplied to ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80. Corrosion behaviour is superior, including marine and chloride environments, the material is largely non-magnetic, and the usable service range is approx. -200 °C to +400 °C, subject to the property class and the joint. In practice this grade is specified for marine, coastal and chemical applications.

- **Grade:** ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80
- **Corrosion resistance:** Superior, including marine and chloride environments
- **Magnetic response:** Largely non-magnetic
- **Service temperature:** approx. -200 °C to +400 °C, subject to the property class and the joint

Property values are typical for the grade. Certified mechanical test data is available on request for production orders.

![A4 (316) Stainless Steel EPDM Rubber Well Nuts reference image](https://engineeringhardware.com/wp-content/uploads/2026/09/EPDM-Rubber-Well-Nuts-Rubber-Blind-Nuts.webp)

A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. Specified on epdm rubber well nuts it determines the corrosion behaviour (superior, including marine and chloride environments) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint); the dimensions are ours rather than a standard's, and are listed in full below.

## Why Choose A4 Stainless Steel for EPDM Rubber Well Nuts

Specified for marine, coastal and chemical applications. For epdm rubber well nuts, this matters when superior, including marine and chloride environments is the primary requirement.

## Mechanical & Physical Properties

| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
| --- | --- |
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |

## Corrosion Behavior in Service

A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For EPDM Rubber Well Nuts in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.

## Galvanic & Galling Considerations

Two important notes for stainless epdm rubber well nuts: (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.

## Using Stainless Fasteners in Aluminum

Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.

## Sizes of EPDM Rubber Well Nuts Available in A4 Stainless Steel

| Thread size | Representative hole diameter (mm) | Representative grip range (mm) | Temperature range (u00b0C) | Representative tightening torque (Nu00b7m) | Body / insert |
| --- | --- | --- | --- | --- | --- |
| M3 | 8.0 | 0.4~4.0 | -30~+80 | 0.5 | EPDM rubber / stainless threaded insert |
| M4 | 8.0 | 0.4~4.0 | -30~+80 | 0.4 | EPDM rubber / stainless threaded insert |
| M5 | 9.7 | 0.4~4.9 | -30~+80 | 0.6 | EPDM rubber / stainless threaded insert |
| M6 | 12.8 | 0.4~4.0 or 0.8~4.7 | -30~+80 | 1.0 | EPDM rubber / stainless threaded insert |
| M8 | 16.0 | 0.4~4.0 | -30~+80 | 1.5 | EPDM rubber / stainless threaded insert |

Dimensions are independent of the material: every size above is available in A4 Stainless Steel.

Custom manufacturing · Made to drawing

## Need this nut in a grade that is not listed?

A4 Stainless Steel is one of the grades the catalog describes. Thread size is the obvious variable and rarely the interesting one — height for clearance, across-flats for the tool already in the cell, and the locking feature for the vibration actually present. 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 M3 EPDM Rubber Well Nuts to Trade series (rubber blind nuts). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Representative hole diameter (mm):** 8.0
- **Representative grip range (mm):** 0.4~4.0
- **Temperature range (u00b0C):** -30~+80
- **Representative tightening torque (Nu00b7m):** 0.5
- **Body / insert:** EPDM rubber / stainless threaded insert

## Dimensions & Specifications (Trade series (rubber blind nuts))

| Thread size | Representative hole diameter (mm) | Representative grip range (mm) | Temperature range (u00b0C) | Representative tightening torque (Nu00b7m) | Body / insert |
| --- | --- | --- | --- | --- | --- |
| M3 | 8.0 | 0.4~4.0 | -30~+80 | 0.5 | EPDM rubber / stainless threaded insert |
| M4 | 8.0 | 0.4~4.0 | -30~+80 | 0.4 | EPDM rubber / stainless threaded insert |
| M5 | 9.7 | 0.4~4.9 | -30~+80 | 0.6 | EPDM rubber / stainless threaded insert |
| M6 | 12.8 | 0.4~4.0 or 0.8~4.7 | -30~+80 | 1.0 | EPDM rubber / stainless threaded insert |
| M8 | 16.0 | 0.4~4.0 | -30~+80 | 1.5 | EPDM rubber / stainless threaded insert |

Product catalog

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[View all Hex & Other Standard Nuts →](https://engineeringhardware.com/fastener-products/nuts/hex-other-standard-nuts/) [Full product catalog](https://engineeringhardware.com/products/)

## Applications & Industries

Where EPDM Rubber Well Nuts are used, and what decides the specification in each case. Stocked from M3 to M8.

### Industries that specify EPDM Rubber Well Nuts

- **Vehicle body panels:** Rubber well nuts isolate and seal trim fasteners through thin skins.
- **Motorcycle service:** Blind rubber inserts provide a thread where the rear face is inaccessible.
- **Outdoor enclosures:** EPDM accommodates panel movement and keeps a small hole sealed.
- **Equipment covers:** Stainless inserts resist corrosion while the rubber body clamps the panel.
- **Maintenance & MRO:** Replacements matched to the existing bolt class, thread and finish.
- **Building services:** Threaded rod, channel and suspension assemblies.

### Typical applications

- adding a blind threaded point to a thin panel
- matching hole diameter and grip range to the EPDM body
- tightening only to the representative torque for the size
- using the rubber body for isolation and sealing
- completing a bolted joint on a stud, rod or bolt
- locking an adjustment so it cannot drift

### Service conditions to specify against

- **Marine and coastal:** Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- **High load:** Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- **Sealed joints:** Used where the fixing has to keep water or air out as well as hold — the elastomer, not the fastener, decides service life.
- **Match the class:** A nut below the bolt property class strips before the bolt reaches its own limit — pair class 8 nuts with 8.8 bolts, class 10 with 10.9.

### Where to use something else

- Do not over-tighten a well nut; excess compression can pull the insert through the panel or damage the seal.

[Full application guide: where EPDM Rubber Well Nuts are used, how to specify them, and the cases they are wrong for](https://engineeringhardware.com/applications/epdm-rubber-well-nuts/)

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

### Can A4 Stainless Steel replace plated alloy steel structurally?

Only at the standard strength classes — A2-70 / A4-80 are roughly equivalent to class 7 steel; A4-100 reaches class 8.8. For class 10.9 or 12.9 strength, plated alloy steel is required.

### Are A4 Stainless Steel EPDM Rubber Well Nuts magnetic?

A4 Stainless Steel EPDM Rubber Well Nuts are largely non-magnetic.

### What corrosion resistance do A4 Stainless Steel EPDM Rubber Well Nuts offer?

A4 Stainless Steel EPDM Rubber Well Nuts provide superior, including marine and chloride environments with a service range of approx. -200 °C to +400 °C, subject to the property class and the joint.

### Should I choose A4 Stainless Steel or A2 (304) for EPDM Rubber Well Nuts?

For EPDM Rubber Well Nuts, A4 Stainless Steel suits general indoor and outdoor use; A2 (304) is preferred for marine, coastal and chemical environments. Choose by corrosion exposure first.

### How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.

## Related Pages

[View the full EPDM Rubber Well Nuts page](https://engineeringhardware.com/fastener/epdm-rubber-well-nuts/)

### More EPDM Rubber Well Nuts Guides