UNC Ring Gauges | McMaster-Carr

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Thread Size

Thread Fit

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Unified Standard Class 3A

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Accuracy Certificate Traceable to NIST

Calibration Certificate Traceable to NIST

Thread Direction

Left Hand

Right Hand

U.S.–Mexico–Canada Agreement (USMCA) Qualifying

Yes

RoHS

Compliant

DFARS Specialty Metals

Exempt

Hardness

Rockwell C60

REACH

Compliant

Export Control Classification Number (ECCN)

EAR99

Material

Tool Steel

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160 Products

Threaded Ring Gauges with Calibration Certificate

Not only were these gauges calibrated in a lab, but they also come with a certificate that's traceable to NIST. The certificate, sometimes called a test report and long form certificate, details the tested measurements. They’re for checking a part’s external threads to ensure they fall within tolerance.

A part is within tolerance if it’s easy to thread a go gauge onto the part but difficult to thread a no-go gauge more than two turns. Inspect faster by holding more than one ring gauge with a threaded ring gauge holder.

Go gauges check the maximum external thread size.

No-go gauges check the minimum external thread size.

Threads have different classes of fit. Thread fit designates the tightness or looseness of the mating threads. For example, inch threads with a 3A fit have tighter tolerances than threads with a 2A fit.

Inch—Class X

Go Gauge
Thread Size	Thread Type	Thread Direction	Hardness	Material	Pitch Dia. Tolerance		Each
For Thread Fit Class 2A
1-64	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A123	0000000
2-56	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A127	000000
3-48	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A132	000000
4-40	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A136	000000
5-40	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A141	000000
6-32	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A145	000000
8-32	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A149	000000
10-24	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A154	000000
12-24	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A158	000000
1/4"-20	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A163	000000
5/16"-18	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A167	000000
3/8"-16	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A172	000000
7/16"-14	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A176	000000
1/2"-13	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A181	000000
9/16"-12	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A409	000000
5/8"-11	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A185	000000
3/4"-10	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A189	000000
7/8"-9	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A194	000000
1"-8	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A198	000000
1 1/8"-7	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0004" to 0"	3160A471	000000
1 1/4"-7	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0004" to 0"	3160A209	000000
1 3/8"-6	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0004" to 0"	3160A473	000000
1 1/2"-6	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0004" to 0"	3160A218	000000
For Thread Fit Class 3A
2-56	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A126	000000
4-40	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A135	000000
5-40	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0002" to 0"	3160A139	000000
6-32	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A144	000000
8-32	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A148	000000
10-24	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A153	000000
1/4"-20	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A162	000000
5/16"-18	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A166	000000
3/8"-16	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A171	000000
1/2"-13	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A179	000000
5/8"-11	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A184	000000
3/4"-10	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A188	000000
7/8"-9	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0003" to 0"	3160A193	000000
1 1/2"-6	UNC	Right Hand	Rockwell C60	Tool Steel	-0.0004" to 0"	3160A217	000000
No-Go Gauge
For Thread Fit Class 2A
1-64	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A225	000000
2-56	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A229	000000
3-48	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A234	000000
4-40	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A238	000000
5-40	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A243	000000
6-32	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A247	000000
8-32	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A252	000000
10-24	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A256	000000
12-24	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A261	000000
1/4"-20	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A265	000000
5/16"-18	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A269	000000
3/8"-16	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A274	000000
7/16"-14	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A278	000000
1/2"-13	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A283	000000
9/16"-12	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A411	000000
5/8"-11	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A287	000000
3/4"-10	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A292	000000
7/8"-9	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A296	000000
1"-8	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A301	000000
1 1/8"-7	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0004"	3160A472	000000
1 1/4"-7	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0004"	3160A312	000000
1 3/8"-6	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0004"	3160A474	000000
1 1/2"-6	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0004"	3160A321	000000
For Thread Fit Class 3A
2-56	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A228	000000
4-40	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A237	000000
5-40	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0002"	3160A242	000000
6-32	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A246	000000
8-32	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A251	000000
10-24	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A255	000000
1/4"-20	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A264	000000
5/16"-18	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A268	000000
3/8"-16	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A273	000000
1/2"-13	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A282	000000
5/8"-11	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A286	000000
3/4"-10	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A291	000000
7/8"-9	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0003"	3160A295	000000
1 1/2"-6	UNC	Right Hand	Rockwell C60	Tool Steel	0" to 0.0004"	3160A319	000000

Threaded Ring Gauges

Check a part’s external threads to make sure they fall within tolerance. You can use these for bolts, threaded rods, bits, and more. All gauges come with a manufacturer’s certificate of accuracy, also known as a certificate of compliance or a short form certification, that verifies the thread sizes are within tolerance.

The part is within tolerance if it’s easy to thread a go gauge onto, but difficult to thread a no-go gauge more than two turns. Use a threaded ring gauge holder to keep two gauges on hand at once for faster inspection.

Go gauges check the maximum external thread size.

No-go gauges check the minimum external thread size.

Inch

Go Gauge
Thread Size	Thread Type	Hardness	Material	Choose a For Thread Fit	Thread Direction	Pitch Dia. Tolerance		Each
Class X
1-64	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0002" to 0"	2356A501	0000000
2-56	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0002" to 0"	2356A304	000000
3-48	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0002" to 0"	2356A113	000000
4-40	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0002" to 0"	2356A308	000000
5-40	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0002" to 0"	2356A311	000000
6-32	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A313	000000
8-32	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A315	000000
10-24	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A317	000000
12-24	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0003" to 0"	2356A121	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A322	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A324	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A326	000000
7/16"-14	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0003" to 0"	2356A127	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A331	000000
9/16"-12	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0003" to 0"	2356A547	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A333	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A335	000000
7/8"-9	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	-0.0003" to 0"	2356A337	000000
1"-8	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0004" to 0"	2356A135	000000
1 1/8"-7	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0004" to 0"	2356A581	000000
1 1/4"-7	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0004" to 0"	2356A138	000000
1 1/2"-6	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0004" to 0"	2356A589	000000
1 3/8"-6	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	-0.0004" to 0"	2356A583	000000
No-Go Gauge
Class X
1-64	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0002"	2356A502	000000
2-56	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0002"	2356A404	000000
3-48	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0002"	2356A613	000000
4-40	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0002"	2356A408	000000
5-40	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0002"	2356A411	000000
6-32	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A413	000000
8-32	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A415	000000
10-24	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A417	000000
12-24	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0003"	2356A721	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A422	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A424	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A426	000000
7/16"-14	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0003"	2356A727	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A431	000000
9/16"-12	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0003"	2356A548	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A433	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A435	000000
7/8"-9	UNC	Rockwell C60	Tool Steel	Class 2A, Class 3A	Right Hand	0" to 0.0003"	2356A437	000000
1"-8	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0004"	2356A735	000000
1 1/8"-7	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0004"	2356A582	000000
1 1/4"-7	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0004"	2356A738	000000
1 1/2"-6	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0004"	2356A591	000000
1 3/8"-6	UNC	Rockwell C60	Tool Steel	Class 2A	Right Hand	0" to 0.0004"	2356A584	000000

Left-Hand Threaded Ring Gauges with Calibration Certificate

Calibrated in a lab and backed by a certificate traceable to NIST, these gauges check if left-hand threads fall within tolerance. The certificate, sometimes called a test report and long-form certificate, details the tested measurements. Use these gauges on screws, threaded rods, and other parts with external threads. For faster tests, hold more than one ring gauge with a threaded ring gauge holder.

Your part is within tolerance if it’s easy to thread a go gauge onto it but difficult to thread a no-go gauge more than two turns.

Go gauges check the maximum external thread size.

No-go gauges check the minimum external thread size.

Thread fit designates the tightness or looseness of mating threads. For inch threads, the higher the class number, the tighter the fit. These metric-threaded ring gauges are class 6g, which is comparable to the fit of those with class 2A threads.

Inch—Class X

Go Gauge
Thread Size	Thread Type	Hardness	Material	Pitch Dia. Tolerance		Each
For Thread Fit Class 2A
6-32	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N31	0000000
8-32	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N32	000000
10-24	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N33	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N34	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N35	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N36	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N37	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N38	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	7836N39	000000
1"-8	UNC	Rockwell C60	Tool Steel	-0.0004" to 0"	7836N41	000000
No-Go Gauge
For Thread Fit Class 2A
6-32	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N73	000000
8-32	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N74	000000
10-24	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N75	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N76	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N77	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N78	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N79	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N81	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	7836N82	000000
1"-8	UNC	Rockwell C60	Tool Steel	0" to 0.0004"	7836N83	000000

Left-Hand Threaded Ring Gauges

Test if the left-hand threads on parts fall within tolerance. These gauges are often used with parts such as screws, bolts, and threaded rods. All come with a manufacturer’s certificate of accuracy, also known as a certificate of compliance or a short-form certification, that verifies the thread sizes are within tolerance.

Go gauges check the maximum external thread size.

No-go gauges check the minimum external thread size.

Inch—Class X

Go Gauge
Thread Size	Thread Type	Hardness	Material	Pitch Dia. Tolerance		Each
For Thread Fit Class 2A
6-32	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N31	0000000
8-32	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N32	000000
10-24	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N33	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N34	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N35	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N36	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N37	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N38	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	-0.0003" to 0"	8399N39	000000
1"-8	UNC	Rockwell C60	Tool Steel	-0.0004" to 0"	8399N41	000000
No-Go Gauge
For Thread Fit Class 2A
6-32	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N73	000000
8-32	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N74	000000
10-24	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N75	000000
1/4"-20	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N76	000000
5/16"-18	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N77	000000
3/8"-16	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N78	000000
1/2"-13	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N79	000000
5/8"-11	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N81	000000
3/4"-10	UNC	Rockwell C60	Tool Steel	0" to 0.0003"	8399N82	000000
1"-8	UNC	Rockwell C60	Tool Steel	0" to 0.0004"	8399N83	000000