4-40 Thread Plug Gauges | McMaster-Carr

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System of Measurement

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Thread Fit

Unified Standard Class 2B

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Accuracy Certificate Traceable to NIST

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UNC

Gauge Measurement Type

No-Go

Thread Direction

Right Hand

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

Yes

Export Control Classification Number (ECCN)

EAR99

Finish

Chrome Plated

Hardness

Rockwell C70

DFARS Specialty Metals

REACH

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8 Products

Go/No-Go Threaded Plug Gauges with Handle

Speed up thread tolerance checks—the handle on these gauges gives you a good grip to quickly thread and unthread go or no-go gauges. Use these gauges to make sure nuts, tapped holes, and other parts fall within tolerance. All are precisely manufactured to confirm thread fit. If the plug gauges wear down, you can insert new ones (not included) onto the taperlock handle.

A part is within tolerance if it’s easy to thread the go gauge into the part but difficult to thread the no-go gauge more than two turns.

Go/no-go gauges have both a go gauge on one end of the handle and a no-go gauge on the other to speed up tests. Go gauges check the minimum internal thread size. No-go gauges check the maximum internal thread size.

Class X Gauge

Double-Ended Taperlock

Handle

Calibration Certificate Traceable to NIST—Gauges with a calibration certificate traceable to NIST were calibrated in a lab. The certificate, sometimes called a test report or long-form certificate, details the tested measurements.

For Class 2B Unified Standard Thread Fit—For inch threads, the higher the class number, the tighter the fit. Unified Standard Class 2B is standard and works for most applications.

For Thread Fit—Thread fit designates the tightness or looseness of mating threads.

	Thread Type	Pitch Dia. Tolerance	Hardness	Material	Features	Choose a Thread Fit		Each
Go/No-Go Gauges



	4-40	UNC	-0.0002" to 0.0002"	Rockwell C70	Chrome-Plated Tool Steel	Double-Ended Taperlock Handle	Unified Standard Class 2B , Unified Standard Class 3B	2366A508	0000000


	Go/No-Go Gauges with Calibration Certificate Traceable to NIST



			4-40	UNC	-0.0002" to 0.0002"	Rockwell C70	Chrome-Plated Tool Steel	Double-Ended Taperlock Handle	Unified Standard Class 2B , Unified Standard Class 3B	3157A17	000000

Threaded Plug Gauges

Test if internal threads fall within tolerance. These plug gauges are often used in nuts and tapped holes to confirm thread fit. For precision and accuracy, they’re manufactured to tight tolerances.

Threads are within tolerance if it’s easy to thread a go gauge but difficult to thread a no-go gauge more than two turns.

Class X Gauge

Go Gauge—Go gauges check the minimum hole diameter.

No-Go Gauge—No-go gauges check the maximum hole diameter.

Accuracy Certificate Traceable to NIST—Gauges with an accuracy certificate traceable to NIST include verification from the manufacturer that their thread sizes are within tolerance. The certificate is also known as a certificate of compliance or a short-form certification.

For Class 2B Unified Standard Thread Fit—For inch threads, the higher the class number, the tighter the fit. Unified Standard Class 2B is standard and works for most applications.

For Thread Fit—Thread fit designates the tightness or looseness of mating threads.

	Thread Type	Pitch Dia. Tolerance	Hardness	Material	For Thread Fit		Each
Go Gauges



	4-40	UNC	0" to 0.0002"	Rockwell C70	Chrome-Plated Tool Steel	Unified Standard Class 2B, Unified Standard Class 3B	7968N13	000000


	Go Gauges with Accuracy Certificate Traceable to NIST



			4-40	UNC	0" to 0.0002"	Rockwell C70	Chrome-Plated Tool Steel	Unified Standard Class 2B, Unified Standard Class 3B	7968N103	00000


			No-Go Gauges



					4-40	UNC	-0.0002" to 0"	Rockwell C70	Chrome-Plated Tool Steel	Unified Standard Class 2B	7968N47	00000


					No-Go Gauges with Accuracy Certificate Traceable to NIST



							4-40	UNC	-0.0002" to 0"	Rockwell C70	Chrome-Plated Tool Steel	Unified Standard Class 2B	7968N137	00000

Go/No-Go Helical Insert Threaded Plug Gauges with Handle

Check that holes tapped for helical threads are within tolerance. You’ll sometimes hear these threads referred to as Screw Thread Insert (STI) threads. To speed up tests, these gauges have a go gauge on one end and a no-go gauge on the other. The double-ended taperlock handle makes them quick to thread and unthread. It also lets you swap in new plug gauges (not included) in place of worn ones.

The go gauge checks the minimum internal thread size, and the no-go gauge checks the maximum. A part is within tolerance if it’s easy to thread the go gauge but difficult to thread the no-go gauge more than two turns.

Plug Gauges with Accuracy Certificate Traceable to NIST—Gauges with an accuracy certificate traceable to NIST include verification from the manufacturer that their thread sizes are within tolerance. The certificate is also known as a certificate of compliance or a short-form certification.

Plug Gauges with Calibration Certificate Traceable to NIST—Gauges with a calibration certificate traceable to NIST were calibrated in a lab. The certificate, sometimes called a test report or long-form certificate, details the tested measurements.

								Plug Gauges with Accuracy Certificate Traceable to NIST		Plug Gauges with Calibration Certificate Traceable to NIST
	Thread Size	Thread Type	Pitch Dia. Tolerance	Hardness	Material	Features	For Thread Fit		Each		Each
Class X Gauge



		4-40	UNC	-0.0002" to 0.0002"	Rockwell C70	Chrome-Plated Tool Steel	Double-Ended Taperlock Handle	Unified Standard Class 2B	7941N12	0000000	7941N29	0000000