Metric ISO-thread ISO 965    Gauge dimensions ISO1502

Tolerance zone Tolerance zone external thread Tolerance zone internal thread
fine 4h 5H
medium for threads 1-1.4mm
for threads > 1.4mm
for threads 1-1.4mm
for threads > 1.4mm
coarse 8g 7H

BSW & BSF threads BS 84    Gauge dimensions BS919

External thread close class medium class free class
Internal thread medium class normal class normal class

Cylindrical pipe threads DIN ISO228 Part1    Gauge dimensions DIN ISO 228 Part 2

Tolerance Class external thread / bolt medium A coarse B
Tolerance Class internal thread / nut medium

ISO metric trapezoidal threads DIN 103    Gauge dimensions DIN 103 Part 9
Tolerance zones group N (normal)

Tolerance Classes Tolerance Zone
external thread
Tolerance Zone
internal thread
medium (m) 7e 7H
coarse (g) 8c 9H

Round thread DIN 405-1, 405-2    Gauge dimensions DIN 405-3
Tolerance zones group N (normal)

Tolerance zone external thread Tolerance zone internal thread
7h and 7e 7H

Unified inch screw threads BS1580    Gauge dimensions BS 919
Tolerance zones group N (normal)

Tolerance zone external thread
External Thread 1A 2A 3A
Internal Thread 1B 2B 3B

Threaded Components

ISO metric threads to BS3643:1981 & BS919 Pt3:1968.

Unified threads to BS1580:1965 & BS919 Pt1:1960


Some Basic Profiles

ISO, UN Threads - BS3643, BS1580

Withworth Threads & G- Series BS84, BS2779

Trapezoidal - BS5436

Round Thread - DIN405

Metric Butress

Butress - BS165X

MJ & UNJ Threads BS6293, BS4084


Gauge Tolerance disposition
- Plug Gauges

Gauge Tolerance disposition
- Ring Gauges

This diagram shows the relationship between product tolerancing and gauge tolerancing. The practice in the UK is to apply tolerances in accordance with BS969:1982 but we can of course supply to other national and international standards.