Precision GO Thread Plug Gauge (Tol. 6H) - M 92 x 6.0

VÖLKEL Precision Thread Go-Gauge (Tol. 6H) – M 92 × 6.0

What is a precision thread go-gauge?
A thread go-gauge is a specialized inspection tool used to check the lower tolerance limit of internal threads (e.g., nuts). It is part of the broader “limit gauge” concept.

Function: The go-gauge represents the smallest acceptable size for the internal thread being checked. Its purpose is to verify that the manufactured thread is not too small (i.e. that the thread flanks have sufficient material and that the core diameter is not undercut).

Precision: The term “precision” emphasizes the extremely high manufacturing accuracy of this gauge. Go-gauges themselves are produced with high precision because they serve as the reference standard for the workpieces being inspected.

Note: Unlike a combined limit gauge (go/no-go) that tests both accept and reject limits, this go-gauge only tests the “go” side. For a complete inspection following the limit gauge principle, a corresponding no-go thread plug gauge would also be required to ensure the thread is not too large.

Where is it used?
Thread go-gauges are essential tools in quality control and manufacturing:

• Quality assurance in production: Used across industries that produce internal threads (e.g., mechanical engineering, automotive, plant engineering, steel construction). They are used for inspection after thread cutting or during incoming goods inspection of supplier parts.

• Workshops and assembly: Used to quickly and easily check whether a freshly cut thread (e.g., after thread repair) or an existing thread (e.g., before screwing in an expensive bolt or shaft) meets minimum size requirements.

• Especially for large threads (M 92 × 6.0): At such large dimensions, precise gauges are essential, as errors can lead to considerable costs or functional failures.

How to use it
The use of a go-thread gauge is standardized and follows this principle:

Preparation:

• Ensure the thread to be checked is clean and free of chips, oil, or dirt.

• Observe the reference temperature of 20 °C (see explanation below). The workpiece and the gauge should ideally be at this temperature.

Inspection process:

• Insert the go-thread gauge into the internal thread of the workpiece.

• Condition: The go-gauge MUST screw in fully by hand (without undue force) through the entire cut thread.

Interpreting the result:

• If the gauge screws in completely: the thread is good in terms of the lower tolerance limit. This means the core diameter and flank diameter are not too small, and the thread flanks are properly formed.

• If the gauge does not screw in fully: the thread is reject. It is too small (e.g., core diameter too tight, flank diameter too small, or deformation).

Tolerance (Tol. 6H)
This designation refers to the tolerance class of the internal thread to be inspected with this gauge.

• 6H: A common and important tolerance class for metric internal threads (nut threads) according to ISO.

• The “6” indicates the tolerance grade—a medium tolerance providing a good balance between precision and manufacturability.

• The “H” denotes the tolerance position or fundamental deviation. “H” means the tolerance zone for the internal thread starts at the nominal size (zero line) and extends toward larger diameters, resulting in a snug to very tight fit with a corresponding external thread (e.g., 6g or 6h).

• A 6H-thread ensures a reliable and functional connection with a matching external thread and is the standard for most metric screw connections.

Why the reference temperature of 20 °C is crucial
The note “Workpieces and gauges refer to a reference temperature of 20 °C” is critical for measurement accuracy:

• Thermal expansion: Metals expand when heated and contract when cooled. Although slight, this effect must be considered in precision measurements where tolerances are in the micrometer range.

• Standardization: 20 °C (68 °F) is internationally established as the standard reference temperature for length measurements (e.g., ISO 1:2002).

• Comparability: By conditioning both the gauge and the workpiece to this temperature, measurement results remain reproducible and comparable, regardless of location or time.

• Avoiding errors: If threads are measured at different temperatures (e.g., a thread at 30 °C measured with a 20 °C gauge), differing expansion levels could lead to misjudgments (a good thread might be rejected if colder, or vice versa).

Conclusion:
The go-thread gauge must screw in by hand (without excessive force) into the internal thread. If it does not, the thread is unacceptable (reject).
Workpieces and gauges must be at 20 °C reference temperature.

As the manufacturer, VÖLKEL can provide a factory calibration certificate upon request. Calibration is carried out in an independent measuring laboratory according to relevant norms and standards (DIN, ISO, ANSI). Calibration is performed on IAC thread scanners.