---
title: "What Are Thread Plug and Ring Gauges Used For?"
description: "Thread Plug and Ring Gauges (ISO 1502 (ISO general purpose metric screw threads — gauging)) are used for installing, adjusting or servicing the assembly ra…"
url: https://engineeringhardware.com/applications/thread-plug-and-ring-gauges/
source: Engineering Hardware & Fasteners
---

# What Are Thread Plug and Ring Gauges Used For?

Tools · ISO 1502 (ISO general purpose metric screw threads — gauging) · Application guide

Typical applications, the industries that specify thread plug and ring gauges, and how to choose the right size, material and finish for the joint.

Thread Plug and Ring Gauges are used for installing, adjusting or servicing the assembly rather than forming part of it. They are manufactured to ISO 1502 (ISO general purpose metric screw threads — gauging), and selection is driven by the nominal size, the fit and tolerance the assembly requires, and the service environment.

- **Primary duty:** Installing, adjusting or servicing the assembly rather than forming part of it
- **Governing standard:** ISO 1502 (ISO general purpose metric screw threads — gauging)
- **Nominal size range:** tolerance class 6g to tolerance class 6g
- **Category:** Tools

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

![What Are Thread Plug and Ring Gauges Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/09/Thread-Plug-And-Ring-Gauges.webp)

Thread Plug and Ring Gauges (ISO 1502 (ISO general purpose metric screw threads — gauging)) are specified where the joint requires installing, adjusting or servicing the assembly rather than forming part of it. 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 6 mm to 6 mm, they cover light-duty and instrument-scale work.

## Typical Applications for Thread Plug and Ring Gauges

The most common settings where these are specified:

- **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment.
- **Maintenance & repair (MRO):** a stocked size for servicing existing plant where the original fastener spec must be matched.
- **Fabrication & metalwork:** bench and on-site assembly of steel frames, enclosures and weldments.

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## How to Specify Thread Plug and Ring Gauges for Your Application

- **Size:** Select on nominal size, and confirm it against the mating feature in the assembly. This product spans 6 mm–6 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 ISO 1502 (ISO general purpose metric screw threads — gauging). Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

## Where Thread Plug and Ring Gauges Are Not the Right Choice

Match the fastener to the load, environment and whether the joint must be reopened; the wrong class or style is the usual cause of joint failure.

Custom manufacturing · Made to drawing

## Need a thread plug and ring gauges outside the standard range?

Dimensions, material, finish and form are specified from the drawing — a fastener tool outside the standard range is a variation on existing tooling rather than a new design.

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

[Custom fastener tool manufacturing](https://engineeringhardware.com/custom/tools/)[Send a drawing](https://engineeringhardware.com/custom/tools/#rfq)

## Technical Drawing

Dimensioned line drawing of thread plug gauge Thread Plug and Ring Gauges to ISO 1502 (ISO general purpose metric screw threads — gauging). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Checks:** internal thread (nuts, tapped holes)
- **GO member:** must screw fully in
- **NO-GO member:** must not enter beyond two turns

## Dimensions & Specifications (ISO 1502 (ISO general purpose metric screw threads — gauging))

| Gauge | Checks | GO member | NO-GO member |
| --- | --- | --- | --- |
| thread plug gauge | internal thread (nuts, tapped holes) | must screw fully in | must not enter beyond two turns |
| thread ring gauge | external thread (bolts, studs) | must screw fully on | must not engage beyond two turns |
| plain plug gauge | drilled hole size before tapping | must enter | must not enter |
| tolerance class 6H | internal thread fit | standard commercial nut thread | standard commercial nut thread |
| tolerance class 6g | external thread fit | standard commercial bolt thread | standard commercial bolt thread |

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

### What are Thread Plug and Ring Gauges used for?

Installing, adjusting or servicing the assembly rather than forming part of it. They are supplied to ISO 1502 (ISO general purpose metric screw threads — gauging).

### Which industries use Thread Plug and Ring Gauges?

They are commonly specified in general machine building, maintenance & repair (mro) and fabrication & metalwork, among other sectors.

### How do I choose the right size of Thread Plug and Ring Gauges?

Select on nominal size and on the fit the assembly requires. This product is available from 6 mm to 6 mm; the full dimension table on this page lists each size.

### Are Thread Plug and Ring Gauges made to a recognized standard?

Yes — they are manufactured to ISO 1502 (ISO general purpose metric screw threads — gauging), so dimensions are interchangeable between suppliers when you quote the standard on your order.

### Can I get a quote for Thread Plug and Ring Gauges 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: [Thread Plug and Ring Gauges — specifications & sizes](https://engineeringhardware.com/fastener/thread-plug-and-ring-gauges/)

### Thread Plug and Ring Gauges Specification Guides

### Related Fastener Applications