Screw Pitch Gauges

About Screw Pitch Gauges

Screw pitch gauges are essential precision measuring tools used to quickly and accurately identify the pitch and thread type of screws, bolts, and threaded fasteners. These ingenious gauges consist of multiple thin metal blades, each stamped with a specific thread profile, which fold into a compact handle similar to a penknife. By matching the gauge blade to the thread you're examining, you can instantly determine whether it's metric, imperial, BSW (British Standard Whitworth), UNC (Unified National Coarse), UNF (Unified National Fine), or another thread standard – saving valuable time and preventing costly mistakes when sourcing replacement fasteners.

Our range includes comprehensive gauge sets from trusted brands including Sealey, Draper, and Faithfull, featuring anywhere from 20 to 55 blades to cover the most commonly encountered thread pitches. Whether you need a compact metric-only gauge for general workshop use or a comprehensive set covering multiple thread standards for specialist engineering work, you'll find options suited to both professional tradespeople and serious DIY enthusiasts. These tools are particularly invaluable when working with older machinery, imported equipment, or legacy fasteners where documentation may be missing or thread standards have changed over the years.

Modern screw pitch gauges are manufactured from hardened steel for durability and long-term accuracy, with clearly marked measurements typically ranging from 0.25mm to 6mm for metric threads, and various TPI (threads per inch) ranges for imperial standards. Many sets include dedicated gauges for specialist applications, with some comprehensive kits like the Sealey 26-piece set also incorporating nut and bolt thread checking capabilities for complete fastener identification.

Jargon Buster

• Thread Pitch: The distance between adjacent threads, measured in millimetres for metric fasteners or threads per inch (TPI) for imperial systems. This critical measurement determines thread compatibility.
• BSW (British Standard Whitworth): A traditional British imperial thread standard still commonly found on older British machinery and vintage vehicles. Uses a 55-degree thread angle and is measured in TPI.
• UNC/UNF (Unified National Coarse/Fine): American imperial thread standards widely used in imported machinery and equipment. UNC threads are coarser with fewer threads per inch, whilst UNF threads are finer for precision applications.
• Metric Thread (M Series): The ISO standard thread system used throughout Europe and increasingly worldwide, designated by the letter M followed by the nominal diameter (e.g., M6, M10) and pitch in millimetres.
• TPI (Threads Per Inch): The imperial measurement system for thread pitch, indicating how many complete threads occur within one inch of fastener length. Higher TPI numbers indicate finer threads.
• Thread Profile: The geometric shape of the thread's cross-section, including its angle, crest, and root dimensions. Different thread standards have distinct profiles that must match for proper engagement.

Who Uses Screw Pitch Gauges?

Screw pitch gauges are indispensable tools across numerous trades and industries:

• Mechanical Engineers – identifying threads on machinery components, hydraulic fittings, and precision equipment
• Motor Vehicle Technicians – determining fastener specifications on vehicles, particularly when working with classic cars or imported models
• Maintenance Engineers – sourcing correct replacement fasteners for plant machinery and production equipment
• Plant Fitters – matching threads on pipework, valves, and industrial equipment during installation and repair
• Agricultural Mechanics – identifying fasteners on farm machinery, which often uses various thread standards
• CNC Machinists – verifying thread specifications during manufacturing and quality control processes
• Model Engineers and Hobbyists – ensuring accurate thread identification for precision engineering projects
• Plumbers – identifying threads on pipe fittings, particularly when working with mixed metric and imperial systems
• General Maintenance Staff – determining correct replacement fasteners across facilities management
• DIY Enthusiasts – particularly those restoring machinery, vehicles, or working with older equipment

How to Choose the Right Screw Pitch Gauges

Thread Standards Required: Consider which thread systems you encounter most frequently. A basic metric-only gauge like the Sealey 20-blade folding gauge suits general workshop applications, whilst engineers working with diverse equipment may need comprehensive sets covering metric, BSW, UNC, UNF, and other standards. The Faithfull 55-blade American-National set or Draper 52-blade combination sets provide extensive coverage for professional environments.

Number of Blades: More blades mean finer increments and better chance of finding an exact match. A 20-blade set covers common pitches adequately for general use, whilst 52-55 blade sets like those from Faithfull and Draper provide comprehensive coverage including less common thread pitches found on specialist or imported equipment.

Build Quality: Professional-grade gauges from Sealey, Draper, and Faithfull feature hardened steel construction that maintains accuracy over years of workshop use. Check that blades are clearly marked and legible – you'll be referencing these measurements frequently. Robust pivot mechanisms ensure blades remain secure and don't become loose with repeated use.

Range Coverage: Verify the pitch range covered suits your applications. Metric gauges typically span 0.25mm to 6mm pitch, whilst imperial gauges cover various TPI ranges. Specialist sets like the Sealey 26-piece nut and bolt thread checking gauge expand functionality beyond simple screw pitch identification.

Portability: Folding designs are compact and pocket-friendly for site work, whilst comprehensive multi-gauge sets in organised cases suit workshop environments where you need quick access to multiple thread standards. Consider whether you need gauges at multiple locations or prefer a single comprehensive set.

Budget Considerations: Basic single-standard gauges represent excellent value for occasional users or those working exclusively with metric fasteners. Comprehensive professional sets require greater investment but eliminate the frustration and time waste of incomplete coverage. For tradespeople, the cost is quickly recovered through reduced fastener identification time and fewer incorrect purchases.

Popular Accessories

• Digital Callipers: Complement pitch gauges by accurately measuring fastener diameters, essential for complete thread specification
• Thread Files: Clean up damaged threads once you've identified the correct pitch, restoring functionality to worn fasteners
• Tap and Die Sets: Create or restore threads matching the specifications identified with your pitch gauge
• Engineers' Squares and Straight Edges: Verify thread alignment and fastener squareness during precision work
• Magnifying Glasses or Loupes: Aid examination of fine threads and reading gauge markings in low-light conditions
• Thread Repair Kits: HeliCoil and similar systems restore stripped threads once you've determined the original specification
• Fastener Assortment Boxes: Organise replacement fasteners by thread type and pitch for efficient workflow

Frequently Asked Questions

What's the difference between metric and imperial thread pitch measurements?

Metric threads measure pitch as the distance between threads in millimetres (e.g., 1.5mm pitch), whilst imperial threads use TPI (threads per inch) – for example, 20 TPI means 20 complete threads within one inch. You cannot interchange these systems; a metric gauge won't accurately measure imperial threads and vice versa. This is why comprehensive sets covering multiple standards are valuable for professional environments.

Can I use a screw pitch gauge on damaged or worn threads?

Whilst screw pitch gauges work best on clean, undamaged threads, experienced users can often identify the original pitch on moderately worn fasteners. Clean the thread thoroughly with a wire brush first, and try matching multiple undamaged sections. If threads are severely damaged, measure the major diameter with callipers and consult thread specification charts alongside your pitch gauge readings for confirmation.

How do I know which thread standard I'm dealing with?

Start by considering the equipment origin and age. British machinery typically uses BSW, European equipment uses metric, and American machinery uses UNC/UNF. Try your metric gauge first on modern equipment; if no blade matches perfectly, move to imperial standards. The gauge blade should mesh completely with the thread profile – partial matches indicate the wrong standard. Equipment manufactured before metrication in the UK (1970s) almost certainly uses imperial threads.

Do I need separate gauges for internal and external threads?

No – screw pitch gauges work equally well on both external threads (bolts, screws) and internal threads (nuts, threaded holes). Simply place the gauge blade against the thread profile; for internal threads, you may need good lighting and positioning to see the match clearly. Some users find it slightly easier to check external threads, but the same gauge serves both purposes.

How should I maintain my screw pitch gauges?

Keep gauges clean and lightly oiled to prevent corrosion, particularly if used in damp workshop environments. Wipe blades after use, especially if you've been checking threads contaminated with oil or cutting fluid. Store in their case to protect against damage – bent blades lose accuracy permanently. Avoid using gauges as prying tools or screwdrivers, despite the temptation. With proper care, quality gauges from Sealey, Draper, and Faithfull provide decades of reliable service.