BS 3409-2:1966

What is BS 3409-2 – Specifications for tapped holes about?  

BS 3409-2 is the second part of the BS 3409 multi-series that discusses the specification for the tapping of holes to receive wire thread inserts. 

BS 3409-2 comprises three sections: 

• Section 1, which specifies limits of size for tapped holes to accommodate wire thread inserts to provide thread sizes from No. 2 to No. 12 UNC and UNF 
• Section 2, which recommends screwing taps intended to produce holes to the limits of the size specified in section 1 
• Section 3, which gives a recommended gauging system for checking the tapped holes 

Who is BS 3409-2 – Specifications for tapped holes for? 

BS 3409-2 on the specification for the tapping of holes to receive wire thread inserts (UNC and UNF threads) is useful for: 

• Manufacturers of drills bits 
• Designers of drill bits 
• Testing and inspection personnel 

Why should you use BS 3409-2 – Specifications for tapped holes?  

A tapped hole is drilled in material or surface where a nut or bolt cannot be used. When a tapped hole is drilled the hole has threads that facilitate the screwing mechanisms. These threads need to be accurate as deformations in them could compromise the screwing mechanism and render the holes useless. 

The guidelines of BS 3409-2 help you to drill tapped holes that are compatible for both UNC and UNF threads. BS 3409-2 also specifies the dimensions for screwing taps that will drill the specified threads. BS 3409-2 also provides guidance on gauging systems that help you to verify dimensions and tolerance for the tapped holes. 

Overall, the guidelines of BS 3409-2 enable you to drill tapped holes with diameters less than 0.25 inches with appropriate UNC and UNF threads.