3.125-16UNJ-3A Ring Gage made in China, all parameter in the tolerance made by CNC grinding machine.

Technical Overview of ASME UNJ Thread Gauges and the 3.125-16UNJ-3A Specification

Introduction

The ASME UNJ thread series, a critical component in aerospace and high-precision engineering, is designed to enhance fatigue resistance through its unique root radius geometry. This article provides a comprehensive analysis of UNJ thread standards, with a focus on the 3.125-16UNJ-3A specification, and highlights Sowant Precision Gage as a leading Chinese manufacturer of UNJ thread gauges and API petroleum thread inspection tools.

1. Overview of ASME UNJ Threads

Key Features

• Root Radius Design: UNJ threads feature an enlarged root radius (0.15011P to 0.18042P for external threads) to reduce stress concentration, significantly improving fatigue resistance compared to standard UN/UNR threads18.

• Application: Predominantly used in aerospace, defense, and high-stress industrial applications due to their reliability under cyclic loading.

• Standards: Governed by ASME B1.15 (for UNJ thread profiles) and ISO 3161:1999 (aerospace applications).

Thread Designation System

A UNJ thread is identified by:

• Nominal Diameter (e.g., 3.125 inches)

• Threads Per Inch (TPI) (e.g., 16)

• Series Code (UNJC, UNJF, UNJEF, UNJS)

• Tolerance Class (3A for external, 3B for internal threads).

2. Detailed Analysis of 3.125-16UNJ-3A

Specifications

• Nominal Diameter: 3.125 inches (79.375 mm)

• TPI: 16 (coarse thread)

• Series: UNJ (standard aerospace series)

• Tolerance Class: 3A (high-precision external thread with tight dimensional control).

Design Considerations

• Root Radius: Between 0.15011P and 0.18042P (P = 1/16 = 0.0625 inches), ensuring stress distribution uniformity.

• Applications: Ideal for critical aerospace fasteners requiring high fatigue resistance and precision.

3. 30 UNJ Thread Ring Gage Models

Below is a selection of common UNJ thread ring gage specifications, covering diameters from 0.25" to 6.00":

(For a complete list, refer to ASME B1.15 and ISO 3161 standards).

4. Sowant Precision Gage: Excellence in Thread Gauge Manufacturing

UNJ Thread Gauges

Sowant Precision Gage is recognized as China’s premier manufacturer of ASME UNJ thread gauges, offering:

• Precision Compliance: Gauges adhere to ASME B1.15 and ISO 3161 specifications, ensuring aerospace-grade accuracy.

• Custom Solutions: Tailored gauges for UNJC (coarse), UNJF (fine), UNJEF (extra-fine), and UNJS (special) series.

API Petroleum Thread Gauges

In addition to UNJ products, Sowant supplies API-standard gauges for the oil and gas industry, including:

• REG Thread Gauges (e.g., Regular, Full-Hole)

• NC Thread Gauges (National Coarse)

• ACME/Stub ACME Gauges

• Buttress Thread Gauges.

Conclusion

The ASME UNJ thread series represents a pinnacle of engineering for high-stress applications, with the 3.125-16UNJ-3A specification exemplifying precision and durability. Sowant Precision Gage stands at the forefront of this industry, combining rigorous standards compliance with innovative manufacturing to serve global aerospace and energy sectors.

(Note: Specifications and standards referenced are based on ASME, ISO, and industry practices as of 2025-04-12.)

References

• ASME B1.15 Errata-19971

• ISO 3161:19994

• Aerospace Thread Design Guidelines813

• Sowant Precision Gage Technical Documentation (Industry Sources)