What is the difference between ANSI B1.2 & ASME B1.2 specifications?

ANSI B1.2 and ASME B1.2 are specifications commonly used in the production and inspection of Unified thread gauges — including UNC, UNF, and other Unified screw thread forms. These standards define how gauges should be manufactured, inspected, and applied to ensure proper thread engagement and interchangeability. From time to time, we receive inquiries where one customer refers to ANSI B1.2, and another mentions ASME B1.2 — raising the question: Are these different specifications? What’s the correct one to follow when ordering Unified gauges?

Let’s clear this up.

ASME/ANSI B1.2 – Gages and Gaging for Unified Inch Screw Threads: One Specification, Two Names

The full and correct name of the standard is:

ASME/ANSI B1.2 – Gages and Gaging for Unified Inch Screw Threads.

This means that the standard was developed by the American Society of Mechanical Engineers (ASME) and officially approved by the American National Standards Institute (ANSI). Although the names differ slightly, there is no difference in the content — they refer to the exact same document.

So whether a drawing or order specifies ANSI B1.2 or ASME B1.2, they both point to the same technical requirements.

What the Specification ASME/ANSI B1.2 Covers

ASME/ANSI B1.2 provides comprehensive guidelines for:

  • Manufacturing and tolerances for plug and ring thread gauges
  • Inspection methods for Unified inch screw threads
  • Limits of size for both internal and external threads

This standard ensures that thread gauges — such as UNC GO/NO-GO plug gauges or thread ring gauges — perform reliably and are compatible across manufacturers.

What This Means for You

Using the correct standard is essential for quality control and part interchangeability. Confusion between ANSI and ASME naming can lead to delays or uncertainty — but now you know: they’re the same specification.

Built to Standard at TruThread Europe

At TruThread Europe, all of our Unified thread gauges are manufactured to ASME/ANSI B1.2, ensuring compliance, durability, and precision for industrial use. We’re committed to delivering gauges you can trust — every time.