Thread Gauges

Thread gauges are precision inspection instruments used to verify that a threaded feature (a tapped hole (internal thread) or a turned/threaded shaft (external thread) ) conforms to its specified dimensional tolerances.

Unlike a micrometer or calliper which give you readings that you must then compare to a specification, a thread gauge gives a direct pass/fail result.

They are the industry-standard method for thread acceptance inspection in production environments, quality control departments and on the shop floor.

Using the correct thread gauge eliminates subjectivity from the inspection process and ensures consistent interchangeability of threaded components.

A go/no-go thread plug gauge (for internal threads) or ring gauge (for external threads) is the standard method for accepting or rejecting threaded components in production:

GO gauge: has dimensions at the minimum material condition (the tightest acceptable thread). It must pass fully through the threaded hole. If it does not pass, the thread is undersize or pitch error is too great - reject

NO-GO gauge: has dimensions at the maximum material condition. It must not pass more than two turns into the thread. If it passes through, the thread is oversized or has excessive pitch error - reject.

This pass/fail method is fast, requires no reading or interpretation and is entirely suitable for production line inspection. We stock thread gauges in Metric Coarse (MC), Metric Fine (MF), Unified Coarse (UNC), Unified Fine (UNF) and Whitworth (G) forms manufactured to DIN and ANSI/ASME standards by Emuge-Franken.

Our Emuge-Franken Thread Gauge range covers:

• DIN ISO 1502: metric thread gauges to the ISO standard, these are the most widely used in Europe & UK manufacturing

• DIN EN ISO 228-2: gauges for pipe threads (G/Whitworth parallel pipe threads)

• ANSI/ASME B1.2: unified thread gauges (UNC/UNF) to the American/imperial standard

Gauges are supplied to DIN 2280 (Go plug), DIN 2281 (No-Go plug), DIN 2283 (Go ring), DIN 2285 (No-Go ring) and DIN 2299 standards. Use the thread form and nominal diameter filters on our listing to find the exact gauge you need.

The type of gauge you need depends on whether you are inspecting an internal or external thread:

• Thread plug gauge: used to inspect internal threads (tapped holes). The gauge member is inserted into the threaded hole. Go/No-Go plug gauges are supplied to DIN 2280 (Go), DIN 2281 (No-Go) and DIN 2283 (No-Go, alternative form)

• Thread ring gauge: used to inspect external threads (bolts, studs, threaded shafts). The threaded component is presented into the ring gauge. Go ring gauges are supplied to DIN 2285 and No-Go rings to DIN 2299.

Both types are available in Go-only, No-Go-only or combined Go/No-Go configurations for every standard thread form in our range.

Our thread gauge range covers all the major international thread standards:

• Metric Course / MC : ISO 68-1 standard metric thread, standard pitch per diameter

• Metric Fine / MF : ISO 68-1 metric thread with reduced pitch for the nominal diameter

• Unified Course / UNC : ANSI/ASME B1.1 imperial thread - standard American pitch series

• Unified Fine / UNF : ANSI/ASME B1.1 imperial thread - fine pitch American series

• Whitworth Parallel Pipe / G : ISO 228-1 / BS EN ISO 228-1 parallel pipe thread (non-pressure-tight)

We stock over 1,800 thread gauge SKUs across all these forms. Use the thread form, nominal diameter and gauge type filters on the listing to navigate directly to the gauge you need.

Both are ISO metric threads with the same thread form angle (60°), but they differ in pitch:

Metric Coarse (MC): each nominal diameter has one standard pitch (e.g. M10 has a pitch of 1.5mm). Coarse threads are the most widely used general-purpose thread in engineering because they are more tolerant of contamination, faster to assemble and more resistant to cross-threading.

Metric Fine (MF): a finer pitch is used for the same nominal diameter (e.g. M10 x 1.25, M10 x 1.0, M10 x 0.75). Fine threads are used where higher clamping loads, resistance to vibration loosening, or precise adjustment is required and are common in aerospace, hydraulics & precision machinery.

A Metric Coarse gauge will not correctly inspect a Metric Fine thread of the same nominal diameter so always ensure you select the correct pitch when ordering.

Both are Unified National (UN) series threads used in American/imperial engineering standards (ANSI/ASME B1.1) with the same 60° thread form:

• Unified National Coarse (UNC): standard pitch for each imperial diameter (e.g., 1/4-20, 3/8-16, 1/2-13). The predominant general-purpose imperial thread for fasteners, fixtures and assemblies

• Unified National Fine (UNF): finer pitch per diameter (e.g., 1/4-28, 3/8-24, 1/2-20). Used in applications requiring greater tensile strength, finer adjustment or improved resistance to vibration.

Our range covers both UNC and UNF in plug and ring gauges to ANSI/ASME B1.2 which is the relevant American gauge standard.

The G thread, also written as (BSP) British Standard Pipe Parallel is defined by ISO 228-1 / DIN EN ISO 228-2. It is a 55° thread form with a specific pitch series measured in threads-per-inch (TPI) and is used for:

• Pipe fittings and hydraulic connections where the seal is achieved by a separate sealing face, O-ring or PTFE tape and not by thread interference

• Common in fluid power, pneumatics and plumbing throughout the UK & Europe

Important distinction: G (parallel pipe) threads should not be confused with Rc/R (BSP Taper) threads, which are not stocked here.

If your application uses tapered pipe threads for pressure-tight joints, confirm the thread form before selecting a gauge - our G thread gauges are manufactured to gauge dimensions according to DIN EN ISO 228-2.

Our thread gauges are manufactured and dimensioned to the relevant DIN standards for thread gauge design:

• DIN 2280: Go thread plug gauges (full form)

• DIN 2281: No-Go thread plug gauges (full form)

• DIN 2283: No-Go thread plug gauges (truncated form, reduced crests)

• DIN 2285: Go thread ring gauges

• DIN 2299: No-Go thread ring gauges

Yes, Emuge-Franken thread gauges are manufactured from high quality aged gauge steel and subject every gauge to 100% dimensional inspection before despatch. Gauges are supplied with manufacturer's certification confirming conformance to the applicable DIN standard and gauge system.

If you require UKAS-accredited calibration certificates (traceable to national standards) for your quality management system or ISO 9001 audit compliance please contact us to discuss calibration options.

Thread gauges are precision instruments and should be handled accordingly:

• Never force a gauge: plugs and rings should move under hand pressure only as forcing a gauge into an undersize thread will damage the gauge and give misleading results

• Keep gauges clean: thread forms must be free of swarf, coolant residue and debris before gauging. Top Tip: a light application of clean oil for storage prevents corrosion!

• Protect from impact: gauge steel is hard but brittle so dropping or knocking gauges against hard surfaces can cause dimensional changes or chipping

• Store correctly: store gauges in their protective cases, away from other cutting tools & abrasive materials and always avoid stacking loose gauges

• Monitor wear: gauges wear in use and will eventually gauge out-of-tolerance so periodic re-calibration against master gauges or inspection by a calibration laboratory will confirm a gauge is still within its working limits

Our range covers an exceptionally broad size range:

• Metric threads: from M1.0 up to M100+ across coarse and fine pitches

• Unified threads: from #0-80 UNF through to 4" UNC

• Whitworth pipe threads: from G 1/8 through to G 6

Both plug gauges and ring gauges are available as individual Go or No-Go gauges or as matched Go/No-Go sets. Use the Nominal Diameter filter on the product listing to locate your required size quickly.