2-1/4-4 Stub Acme-2G

ASME B1.8 Stub Acme Thread Gauges: Essential Parameters, Gauging Principles, and the Expertise of China‘s Sowant Precision Gage

1. Introduction to ASME B1.8 and Stub Acme Thread Gauges

The ASME B1.8 standard, formally titled Stub Acme Screw Threads, defines a specialized thread form that emerged in the early 1900s to address a critical engineering need: applications where a coarse-pitch thread of shallow depth is required due to mechanical or structural considerations [4†L4-L7]. Unlike standard Acme threads (ASME B1.5), which have a basic thread height of 0.5 times the pitch (0.5p), Stub Acme threads feature a reduced height of only 0.3 times the pitch (0.3p) [3†L5-L6][10†L23-L24].

This shallower profile makes Stub Acme threads ideal for thin-walled applications where standard Acme threads cannot be used—such as tubing in oilfield equipment, aerospace components, and heavy machinery traversing mechanisms [6†L13-L16][5†L7-L9]. The 29° thread angle remains identical to standard Acme threads, ensuring compatibility with existing manufacturing tooling while providing a broader, stronger thread form than conventional 60° V-shaped threads [19†L28-L29].

Stub Acme thread gauges are precision-manufactured functional inspection tools used to verify that internal and external Stub Acme threads conform to the dimensional requirements and tolerances mandated by ASME B1.8. These gauges are available as plug gauges (for inspecting internal threads) and ring gauges (for inspecting external threads), manufactured in diameter ranges from 1/4″ up to 14″ or larger, with TPI (threads per inch) ranging from 2 to 16 [5†L11-L12].

2. Fundamental Parameters of ASME B1.8 Stub Acme Threads

2.1 Core Thread Geometry

All ASME B1.8 Stub Acme threads share a common foundational geometry regardless of nominal diameter:

The 2G class is the most commonly specified for general usage, corresponding to the General Purpose Acme thread class defined in ASME B1.5. When a fit with less backlash is required, tolerances for 3G or 4G classes may be applied [4†L18-L20][10†L21-L23].

2.2 Basic Dimensions of Stub Acme Thread Form

The following table presents the basic dimensional formulas and values for the most common Stub Acme thread pitches as defined in ASME B1.8-1988:

*Source: Machinery‘s Handbook 27th Edition — ASME/ANSI B1.8-1988 (R2001) Table 13* [7†L36-L43]

2.3 Stub Acme Thread Series (Selected Diameters and Pitches)

The following selected series represents the most commonly encountered Stub Acme thread sizes, including the nominal major diameter and corresponding pitch diameter:

Source: HEMCO Gage — Stub Acme Gaging Technical Data [4†L27-L35]

3. Detailed Specifications: 2-1/4-4 Stub Acme-2G Thread Plug Gauge

The 2-1/4-4 Stub Acme-2G thread plug gauge is a representative example of a medium-large diameter Stub Acme gauge used in heavy-duty power transmission and thin-wall tubing applications. Below are the complete engineering specifications for this gauge.

3.1 Nominal Designation Interpretation

3.2 Basic Dimensional Parameters

Pitch Diameter Calculation:
Basic Pitch Diameter = Nominal Major Diameter — Basic Thread Height
= 2.2500 — 0.0750 = 2.1750 inches

Minor Diameter Calculation:
Basic Minor Diameter = Nominal Major Diameter — (2 × Basic Thread Height)
= 2.2500 — 0.1500 = 2.1000 inches

Note: The basic minor diameter (2.1000″) represents the theoretical diameter at the thread root for an external thread—or the bore diameter for an internal thread.

3.3 2G Class Tolerance Specifications

For a 2-1/4-4 Stub Acme-2G plug gauge (used to inspect internal threads such as nuts), the working gauge dimensions are derived from ASME B1.8, which adopts pitch diameter tolerances consistent with ASME B1.5 Class 2G General Purpose Acme threads [7†L15-L20].

3.4 Physical Gauge Specifications

3.5 Acceptance Criteria (Gauging Rules)

When inspecting an internal Stub Acme thread using the 2-1/4-4 Stub Acme-2G plug gauge:

• GO end: Must pass through the full length of the internal thread by hand, without excessive force [10†L27-L28]

• NO-GO end: Must NOT enter the internal thread by more than 2 to 3 turns from either end [12†L44-L45][18†L23-L25]

If either condition fails, the threaded component is considered non-conforming.

3.6 Comparison with Adjacent Standard Sizes

For context, here are the basic dimensions of Stub Acme thread sizes surrounding 2-1/4″:

Source: Derived from HEMCO Gage selected series table for 4 TPI and 3 TPI Stub Acme threads [4†L29-L35]

4. Principles and Methods of Gauging Stub Acme Threads per ASME B1.8

ASME B1.8 specifies detailed requirements for gauging Stub Acme screw threads, including both GO/NO-GO functional gauging and individual element inspection.

4.1 GO / NO-GO Functional Gauging

The functional gauging method is the primary acceptance method for Stub Acme threads. It uses a GO gauge and a NO-GO gauge to verify that the product thread’s functional size—including the combined effects of pitch diameter, lead, flank angle, and taper—remains within specified limits [5†L8-L12].

Working principle:

The NO-GO gauge primarily inspects the pitch diameter, confirming it does not exceed the maximum allowable condition. In the case of plug gauges, the major diameter is not directly checked by the NO-GO member, while the minor diameter requires separate verification [18†L43-L45].

4.2 Gauging Rules (Acceptance Criteria)

These rules are consistent with general thread gauging practices specified in ASME B1.2 for UN series threads and are applied to Stub Acme threads per ASME B1.8 [18†L33-L35][18†L6-L9].

4.3 Three-Wire Method for Pitch Diameter Measurement

Appendix B of ASME B1.8 describes the three-wire method for measuring the pitch diameter of 29° Stub Acme threads. This method uses precision-ground wires of a specific diameter placed between the thread flanks, with measurements taken over the wires using a micrometer [9†L11-L13].

Advantages of the three-wire method:

• Provides direct measurement of actual pitch diameter

• Essential for calibrating working plug and ring gauges

• Enables verification of intermediate thread dimensions beyond functional GO/NO-GO inspection

• Particularly useful for multi-start Stub Acme threads

4.4 Recommended Gauging Sequence

For complete thread inspection in production environments, the following sequence is recommended:

1. GO gauge test — Establishes that the minimum material condition is satisfied

2. NO-GO gauge test — Verifies that the maximum material condition is not exceeded

3. Pitch diameter verification (using three-wire method or dedicated pitch diameter instrument) — Provides quantitative measurement data

4. Lead and flank angle inspection — Performed on sample basis using specialized instruments

5. Minor diameter (internal) or major diameter (external) verification — Using plain plug or ring gauges

Master gauges (setting plugs and setting rings) are used to calibrate working GO and NO-GO gauges periodically to account for wear. Wear check plugs are used to monitor the condition of used GO ring gauges [6†L16-L18].

5. Applications of Stub Acme Threads and Gauges

Stub Acme threads find extensive application across diverse industrial sectors due to their unique combination of coarse pitch and shallow depth.

5.1 Primary Application Areas

5.2 Why Choose Stub Acme Over Standard Acme?

Stub Acme threads retain the 29° trapezoidal form, which provides greater strength and wear resistance compared to standard 60° V-threads, while the reduced thread height allows their use in applications where standard Acme threads would risk wall penetration or mechanical failure.

6. Sowant Precision Gage — China‘s Leading Stub Acme Thread Gauge Manufacturer

6.1 Company Profile

Sowant Precision Gage Co., Ltd. (苏州斯文克精密测量设备有限公司) , established in 2012, has evolved into a premier manufacturer and supplier of precision thread gauges in China [14†L22-L23]. Headquartered in the newly developed Wusong River Business District in Suzhou, the company has built a reputation for engineering excellence, manufacturing precision, and responsive customer service.

Sowant manufactures a comprehensive range of threaded and plain cylindrical plug gauges in a variety of materials—including chrome-plated, tin-coated, carbide, ceramic, and other specialized materials—as well as special gauges including pre-plates, multiple-start threads, special leads, and acme thread gauges [14†L33-L37].

6.2 Stub Acme Thread Gauge Product Portfolio

Sowant Precision Gage is a recognized manufacturer and supplier of ASME B1.8 Stub Acme thread gauges, offering both plug gauges and ring gauges in sizes ranging from 1/4″ to 14″ and larger, with TPI from 2 to 16 [15†L19-L20]. Their product range includes:

Stub Acme thread gauges are available in tolerance classes 2G, 3G, and 4G, accommodating both general-purpose applications and those requiring reduced backlash.

6.3 The 2-1/4-4 Stub Acme-2G Thread Plug Gauge — Available from Stock

Sowant Precision Gage maintains a substantial inventory of Stub Acme thread gauges, including the 2-1/4-4 Stub Acme-2G GO & NO-GO plug gauge set. These gauges are manufactured in strict accordance with ASME B1.8 specifications, featuring:

• Precision-ground 29° Stub Acme thread form

• GO end pitch diameter: Basic + allowance per ASME B1.8 Table 4

• NO-GO end pitch diameter: Maximum permissible per ASME B1.8 tolerance tables

• High-carbon tool steel construction, heat-treated to 58–62 HRC

• Double-ended design for convenient GO/NO-GO operation

• Clear laser engraving with full designation (example: “2-1/4-4 STUB ACME-2G GO”)

• Supplied with individual protective case and calibration certificate

The company welcomes inquiries regarding this gauge type, including quantity discounts, expedited delivery options, and custom specifications.

6.4 Quality Assurance and Calibration

Every Stub Acme thread gauge manufactured by Sowant undergoes rigorous quality control before shipment:

1. Inspection by Master Gauges — All working gauges are verified against master/calibration grade gauges traceable to national and international standards

2. Hardness Testing — Verification of 58–62 HRC for wear resistance and dimensional stability

3. Surface Finish Measurement — Ground thread flanks with ≤0.2 μm Ra for smooth gauging action

4. Calibration Certificate — Provided with every gauge, traceable to recognized standards (ISO, DIN, GB)

Sowant collaborates with recognized testing organizations, including Aerospace Metrology and Huasu Inspection, to provide repair and calibration services for adjustable thread ring gauges and plug gauges.

6.5 Strategic Partnerships and Global Reach

Sowant Precision Gage distinguishes itself through strategic partnerships with leading international gauge brands. The company serves as the official authorized distributor for Mitutoyo in China, providing full sales and technical support for Mitutoyo’s complete product line. Additionally, Sowant partners with Mahr, Gagemaker, and Insize,Diatest,Schwenk Bore gage,Trimos,Sylvac, offering customers a comprehensive range of imported thread gauges alongside their domestically manufactured products.

This dual capability—manufacturing high-quality China-made thread gauges while distributing top-tier international brands—positions Sowant as a uniquely trusted partner for both domestic and global customers.

6.6 Why Choose Sowant Precision Gage for Stub Acme Thread Gauges?

6.7 Contact Information

Sowant Precision Gage Co., Ltd. welcomes inquiries from customers worldwide. For pricing, availability, technical specifications, and custom manufacturing requests—including the 2-1/4-4 Stub Acme-2G plug gauge—please contact:

SOWANT PRECISION GAGE CO., LTD.
Wusong River Business District, Suzhou, China
Email / Website: www.swttool.com
Thread Gages Manufacture · Acme Thread Gauges · API Thread Gages · Stub Acme Thread Gauges

7. Conclusion

The ASME B1.8 Stub Acme thread gauge standard provides the essential framework for quality assurance of shallow-depth, coarse-pitch threaded connections across oil and gas, aerospace, heavy machinery, and thin-wall tubing applications. The Stub Acme thread form—with its 29° included angle, 0.3P thread height, and compatibility with 2G, 3G, and 4G fit classes—offers engineers a robust solution where standard Acme threads cannot be applied due to wall thickness constraints.

The 2-1/4-4 Stub Acme-2G thread plug gauge exemplifies the precision required in Stub Acme gauging, with basic dimensions of 2.2500″ major diameter, 2.1750″ pitch diameter, and 2.1000″ minor diameter at 4 TPI. Proper gauging practice requires GO end acceptance (full thread passage) and NO-GO end rejection (no more than 2 to 3 turns of entry), as specified by ASME B1.8.

Sowant Precision Gage Co., Ltd. stands as a premier manufacturer and supplier of ASME B1.8 Stub Acme thread gauges, including the 2-1/4-4 Stub Acme-2G plug gauge available directly from inventory. With in-house manufacturing capabilities covering a full range of thread gauges—from 1/4″ to 14″ diameters, 16 to 2 TPI, and 2G, 3G, 4G tolerance classes—backed by traceable calibration, ISO-compliant quality assurance, and strategic international partnerships, Sowant delivers the precision, reliability, and responsiveness that demanding industrial applications require.

For inquiries, quotations, or technical consultation regarding Stub Acme thread gauges, contact Sowant Precision Gage today.

*Disclaimer: Product specifications, dimensional data, and tolerance values are based on ASME B1.8-1988 (R2001), Machinery‘s Handbook 27th Edition, and publicly available technical data from leading gauge manufacturers. Specifications are subject to change without notice. Customers are advised to confirm specific requirements with Sowant Precision Gage prior to ordering.*