BS ISO 965-3:2021

What is ISO 965‑3 about?  

ISO 965‑3 is the third part of the ISO 965‑3 multi-series. ISO 965‑3 specifies limit deviations for pitch and crest diameters for ISO general purpose metric screw threads (M) conforming to ISO 261 having a basic profile by ISO 68-1.  

The limit deviations specified are derived from the fundamental deviations and tolerances specified in ISO 965-1. 

ISO 965‑3 applies to ISO general purpose metric screw threads with the recommended tolerance classes. 

Who is ISO 965‑3 for?  

ISO 965‑3 on limit deviations for screw threads is relevant to:  

• Manufacturer and supplier of metric screw threads 
• Design and project engineers 
• Mechanical industries 

Why should you use ISO 965‑3?  

The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. The "M" designation for metric screws indicates the nominal outer diameter of the screw thread, in millimetres.  

ISO 965‑3 provides limit deviations which includes design principles including basic major diameter, pitch diameter, minor diameter and tolerance class of ISO metric screw thread. 

This information provided by ISO 965‑3 is helpful for you to attain compliance with superior design and manufacturing practices for screw threads, thus meeting the requirements of your specific engineering needs. 

What’s changed since the last update?  

BS ISO 965‑3:2021 supersedes BS ISO 965‑3:1998, which is withdrawn. The main changes compared to the previous edition are as follows: 

• In the document title, “constructional” has been deleted 
• Scope is updated 
• In limit deviations, the phrase “basic profiles” has been replaced by “basic profile and fundamental deviation” 
• In the limit deviations and limit deviations table, the deviation formula and values for the minor diameter of external threads have been deleted 
• In the limit deviations table four tolerance classes (4g, 5g4g, 8e and 9e8e) have been added