Left-Hand-Thread Ring Gauges

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Thread Size

Thread Direction

Thread Fit

Unified Standard Class 2A

Unified Standard Class 3A

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Metric

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Gauge Measurement Type

No-Go

Certificate Type

Accuracy Certificate Traceable to NIST

Calibration Certificate Traceable to NIST

Material

Tool Steel

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

Yes

Hardness

Rockwell C60

RoHS

Compliant

DFARS Specialty Metals

Exempt

Export Control Classification Number (ECCN)

EAR99

REACH

Compliant

Size-Checking Gauge Class

Pitch

152 Products

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.

Class X Gauges

Go Gauge—Go gauges check the maximum external thread size.

No-Go Gauge—No-go gauges check the minimum external thread size.

For Thread Fit—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 unified standard class 2A threads.

						Go Gauge			No-Go Gauge
	Thread Size	Thread Direction	Hardness	Material	Certificate Type	Pitch Dia. Tolerance		Each	Pitch Dia. Tolerance		Each
For Class 2A Unified Standard Thread Fit







				UNC Thread

				6-32	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N31	0000000	0" to 0.0003"	7836N73	0000000


				8-32	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N32	000000	0" to 0.0003"	7836N74	000000
				10-24	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N33	000000	0" to 0.0003"	7836N75	000000
				1/4"-20	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N34	000000	0" to 0.0003"	7836N76	000000
				5/16"-18	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N35	000000	0" to 0.0003"	7836N77	000000
				3/8"-16	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N36	000000	0" to 0.0003"	7836N78	000000
				1/2"-13	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N37	000000	0" to 0.0003"	7836N79	000000
				5/8"-11	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N38	000000	0" to 0.0003"	7836N81	000000
				3/4"-10	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N39	000000	0" to 0.0003"	7836N82	000000
				1"-8	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0004" to 0"	7836N41	000000	0" to 0.0004"	7836N83	000000




						UNF Thread

						10-32	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N11	000000	0" to 0.0003"	7836N53	000000


						1/4"-28	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N13	000000	0" to 0.0003"	7836N55	000000
						5/16"-24	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N15	000000	0" to 0.0003"	7836N57	000000
						3/8"-24	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N17	000000	0" to 0.0003"	7836N59	000000
						7/16"-20	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N19	000000	0" to 0.0003"	7836N62	000000
						1/2"-20	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N22	000000	0" to 0.0003"	7836N64	000000
						5/8"-18	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N24	000000	0" to 0.0003"	7836N66	000000
						3/4"-16	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N26	000000	0" to 0.0003"	7836N68	000000
						1 1/4"-12	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N28	000000	0" to 0.0003"	7836N71	000000


						For Class 3A Unified Standard Thread Fit







										UNF Thread

										10-32	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N12	000000	0" to 0.0003"	7836N54	000000


										1/4"-28	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N14	000000	0" to 0.0003"	7836N56	000000
										5/16"-24	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N16	000000	0" to 0.0003"	7836N58	000000
										3/8"-24	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N18	000000	0" to 0.0003"	7836N61	000000
										7/16"-20	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N21	000000	0" to 0.0003"	7836N63	000000
										1/2"-20	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N23	000000	0" to 0.0003"	7836N65	000000
										5/8"-18	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N25	000000	0" to 0.0003"	7836N67	000000
										3/4"-16	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N27	000000	0" to 0.0003"	7836N69	000000
										1 1/4"-12	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.0003" to 0"	7836N29	000000	0" to 0.0003"	7836N72	000000


										For Class 6g Metric Thread Fit







										Metric Thread

										M5 × 0.8 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N42	000000	0 mm to 0.008 mm	7836N84	000000


										M6 × 1 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N43	000000	0 mm to 0.008 mm	7836N85	000000
										M8 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N44	000000	0 mm to 0.008 mm	7836N86	000000
										M10 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N45	000000	0 mm to 0.008 mm	7836N87	000000
										M10 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N46	000000	0 mm to 0.008 mm	7836N88	000000
										M12 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N47	000000	0 mm to 0.008 mm	7836N89	000000
										M12 × 1.75 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N48	000000	0 mm to 0.008 mm	7836N91	000000
										M14 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N49	000000	0 mm to 0.008 mm	7836N92	000000
										M16 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N51	000000	0 mm to 0.008 mm	7836N93	000000
										M16 × 2 mm	Left Hand	Rockwell C60	Tool Steel	Calibration Certificate Traceable to NIST	-0.008 mm to 0 mm	7836N52	000000	0 mm to 0.008 mm	7836N94	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.

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.

Class X Gauges

Image of Product. Front orientation. Ring Gauges. Left-Hand Threaded Ring Gauges.

Go Gauge—Go gauges check the maximum external thread size.

No-Go Gauge—No-go gauges check the minimum external thread size.

						Go Gauge			No-Go Gauge
	Thread Size	Thread Direction	Hardness	Material	Certificate Type	Pitch Dia. Tolerance		Each	Pitch Dia. Tolerance		Each
For Class 2A Unified Standard Thread Fit







				UNC Thread

				6-32	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N31	0000000	0" to 0.0003"	8399N73	0000000


				8-32	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N32	000000	0" to 0.0003"	8399N74	000000
				10-24	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N33	000000	0" to 0.0003"	8399N75	000000
				1/4"-20	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N34	000000	0" to 0.0003"	8399N76	000000
				5/16"-18	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N35	000000	0" to 0.0003"	8399N77	000000
				3/8"-16	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N36	000000	0" to 0.0003"	8399N78	000000
				1/2"-13	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N37	000000	0" to 0.0003"	8399N79	000000
				5/8"-11	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N38	000000	0" to 0.0003"	8399N81	000000
				3/4"-10	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N39	000000	0" to 0.0003"	8399N82	000000
				1"-8	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0004" to 0"	8399N41	000000	0" to 0.0004"	8399N83	000000




						UNF Thread

						10-32	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N11	000000	0" to 0.0003"	8399N53	000000


						1/4"-28	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N13	000000	0" to 0.0003"	8399N55	000000
						5/16"-24	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N15	000000	0" to 0.0003"	8399N57	000000
						3/8"-24	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N17	000000	0" to 0.0003"	8399N59	000000
						7/16"-20	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N19	000000	0" to 0.0003"	8399N62	000000
						1/2"-20	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N22	000000	0" to 0.0003"	8399N64	000000
						5/8"-18	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N24	000000	0" to 0.0003"	8399N66	000000
						3/4"-16	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N26	000000	0" to 0.0003"	8399N68	000000
						1 1/4"-12	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N28	000000	0" to 0.0003"	8399N71	000000


						For Class 3A Unified Standard Thread Fit







										UNF Thread

										10-32	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N12	000000	0" to 0.0003"	8399N54	000000


										1/4"-28	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N14	000000	0" to 0.0003"	8399N56	000000
										5/16"-24	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N16	000000	0" to 0.0003"	8399N58	000000
										3/8"-24	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N18	000000	0" to 0.0003"	8399N61	000000
										7/16"-20	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N21	000000	0" to 0.0003"	8399N63	000000
										1/2"-20	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N23	000000	0" to 0.0003"	8399N65	000000
										5/8"-18	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N25	000000	0" to 0.0003"	8399N67	000000
										3/4"-16	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N27	000000	0" to 0.0003"	8399N69	000000
										1 1/4"-12	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.0003" to 0"	8399N29	000000	0" to 0.0003"	8399N72	000000


										For Class 6g Metric Thread Fit







										Metric Thread

										M5 × 0.8 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N42	000000	0 mm to 0.008 mm	8399N84	000000


										M6 × 1 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N43	000000	0 mm to 0.008 mm	8399N85	000000
										M8 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N44	000000	0 mm to 0.008 mm	8399N86	000000
										M10 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N45	000000	0 mm to 0.008 mm	8399N87	000000
										M10 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N46	000000	0 mm to 0.008 mm	8399N88	000000
										M12 × 1.25 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N47	000000	0 mm to 0.008 mm	8399N89	000000
										M12 × 1.75 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N48	000000	0 mm to 0.008 mm	8399N91	000000
										M14 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N49	000000	0 mm to 0.008 mm	8399N92	000000
										M16 × 1.5 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N51	000000	0 mm to 0.008 mm	8399N93	000000
										M16 × 2 mm	Left Hand	Rockwell C60	Tool Steel	Accuracy Certificate Traceable to NIST	-0.008 mm to 0 mm	8399N52	000000	0 mm to 0.008 mm	8399N94	000000