BS 3409-2 – Specification for the tapping of holes to receive wire thread inserts (UNC and UNF threads). Diameters below 3/16 in
Limits of size for tapped holes to accommodate wire thread inserts to provide thread sizes from No. 2 to No. 12 UNC inclusive and from No. 2 to No. 12 UNF inclusive. Recommendations for general dimensions and limits of size on the threaded portion of screwing taps intended to produce holes to the limits specified; details of a recommended gauging system for checking them.
