Check Clearances, Threads, Radii & Bores

When a component needs more than a quick dimensional check, Spear & Jackson precision gauges give machinists, fitters, mechanics, fabricators & maintenance teams purpose-built options for checking clearances, thread pitches, radii, bores, drill sizes & other workshop dimensions. The range includes feeler gauges, screw-pitch gauges, radius gauges, bore gauges, drill gauges & wire gauges for inspection tasks where the measuring method needs to match the feature being checked.

Need a direct dimensional reading rather than a comparison gauge? Spear & Jackson | Precision Measurement Tools - Calipers covers inside, outside, digital & spring-joint calipers while Spear & Jackson | Engineering Tools supports related marking, punching, tapping, fitting & workshop inspection work.

Start with the feature rather than the tool name. A feeler gauge checks a narrow clearance, a screw-pitch gauge identifies or compares thread pitch, a radius gauge matches curved profiles & a bore gauge addresses an internal feature. Similar workshop tasks can therefore require completely different gauge geometry.

What Are Spear & Jackson Precision Gauges?

Precision gauges are inspection tools designed around specific workshop dimensions, profiles or tolerance checks.

The live Industrial Shed collection includes product types such as:

► Feeler gauges
► Radius gauges
► Bore gauges
► Drill gauges
► Wire gauges
► Screw-pitch gauges
► Screw-cutting gauges
► Thread-reference gauges
► Metric gauge sets
► Imperial gauge sets
► Multi-standard gauge sets

Not every gauge provides a conventional numerical measurement in the same way as a caliper. Some gauges identify a matching profile, some compare a known blade thickness against a gap & others help confirm whether a feature corresponds with a defined size or standard.

Why Choose Spear & Jackson Precision Gauges?

A specialised gauge can answer a workshop question more directly than trying to adapt a general measuring tool to the feature.

The current collection includes dedicated gauges for:

► Gap & clearance checking
► Thread-pitch identification
► Radius comparison
► Bore inspection
► Drill-size checking
► Wire-size checking
► Machining setup
► Mechanical servicing
► Component identification
► Workshop inspection

The correct gauge depends on the information required. A 0.20mm clearance, 1.5mm thread pitch & 5mm radius are all dimensions, but each calls for a different contact method.

Common Applications

Where does the uncertainty sit — between two surfaces, around a curved edge, inside a bore or along a thread?

Precision gauges can support:

► Automotive servicing
► Machinery maintenance
► Mechanical fitting
► Machining
► Fabrication
► Thread identification
► Engine clearance checking
► Component inspection
► Bore verification
► Radius matching
► Drill identification
► Wire-size checking
► Workshop repairs
► Production inspection

Choosing the gauge around the actual feature can simplify the inspection. Instead of trying to interpret a difficult caliper reading inside a narrow gap, for example, a calibrated feeler blade can directly test whether that clearance will accept a known thickness.

Product Selection Guide

Identify what needs checking before comparing individual gauge sets.

Don't make the most familiar measuring tool do every inspection job. Selecting by measuring principle can improve both access & confidence in the result.

Feeler Gauges

Some of the most important workshop dimensions exist in spaces too narrow for ordinary caliper jaws.

Feeler gauges use blades of known thickness to check clearances between suitable mating surfaces or mechanical components. Industrial Shed currently lists 18 feeler-gauge products within this collection.

Current Spear & Jackson examples include:

► MW-911M-10-B Safe & Sure 100mm 10-blade set
► MW-395M-20-A Precision 150mm 20-blade set
► MW-399M-20-A Precision 300mm 20-blade set
► Imperial precision 6" 10-blade sets

Blade count & blade length don't tell you the complete measurement range. Check the individual blade thicknesses before choosing a set for a particular mechanical clearance.

When to Use Feeler Gauges

A feeler gauge becomes useful when the question is “what thickness fits this gap?”

Suitable applications can include:

► Mechanical clearances
► Engine servicing
► Machinery setup
► Component spacing
► Assembly checks
► Workshop inspection

Use light contact rather than forcing a blade into the gap. A blade that only enters after bending or excessive pressure may not represent the actual clearance being checked.

Feeler Gauges vs Calipers

Both measure dimensions, but they approach narrow clearances from opposite directions.

Feature accessibility should decide between them. For broader dimensional checks, Spear & Jackson | Precision Measurement Tools - Calipers provides the related caliper range.

Screw-Pitch Gauges

A threaded component can have the correct diameter & still be completely incompatible when the pitch is wrong.

Screw-pitch gauges use individual profile blades to compare against thread spacing.

The current range includes:

► ISO Metric 22-blade gauge — MW-809
► Unified 30-blade gauge — MW-806
► S.I. Metric 30-blade gauge — MW-801
► Whitworth 28-blade gauge — MW-800
► American National 30-blade gauge — MW-799
► S.I. Metric & Whitworth 49-blade gauge — MW-804

Thread standard belongs at the centre of the decision. A gauge designed around Metric pitch isn't interchangeable with a Whitworth or Unified reference simply because the component diameter looks similar.

Metric Thread-Pitch Gauges

Metric threads are identified by pitch in millimetres rather than threads per inch.

An ISO Metric or S.I. Metric pitch gauge can help compare an existing thread against known pitch profiles.

Useful situations include:

► Identifying unmarked fasteners
► Checking replacement hardware
► Mechanical maintenance
► Machinery repair
► Workshop sorting
► Threading preparation

Diameter still needs checking separately. A pitch gauge can help identify spacing between threads but doesn't automatically establish the complete fastener specification.

For related hardware, Bolts & Fasteners provides a relevant next step once thread size, pitch & other requirements are established.

Unified Thread Gauges

Imperial-looking fasteners can still belong to different thread systems.

Unified thread standards include familiar UNC & UNF configurations, where diameter plus threads per inch determine the specification.

A Unified screw-pitch gauge can help compare the existing thread against compatible pitch profiles.

Don't identify an imperial fastener from diameter alone. For example, two fasteners with the same nominal diameter can carry different TPI values & require completely different mating hardware.

Whitworth Thread Gauges

Older machinery, imported equipment & legacy assemblies can introduce Whitworth threads where modern Unified assumptions create confusion.

The Spear & Jackson range includes dedicated Whitworth pitch gauges plus combination Metric & Whitworth configurations.

Before selecting replacement hardware:

► Identify thread system
► Check nominal diameter
► Compare pitch
► Inspect thread condition
► Confirm component application

Similar-looking imperial threads aren't proof of interchangeability. Use the correct thread reference before replacing or machining components.

Screw-Cutting Gauges

Setting up thread-cutting work requires more than knowing how far apart the thread peaks are.

The collection includes the MW-200 Traditional Screw Cutting Gauge, intended as a workshop reference around screw-cutting operations.

A screw-cutting gauge can assist when:

► Preparing lathe threading work
► Checking thread-tool geometry
► Setting tool orientation
► Working with defined thread forms

Keep thread-pitch identification & cutting-tool setup as separate questions. Different gauges can support different stages of the threading process.

Radius Gauges

Curved profiles are difficult to judge accurately by eye once the difference between two radii becomes small.

Radius gauges use known curved profiles for comparison against suitable internal or external radii.

Industrial Shed currently lists 16 radius-gauge products in the collection.

Metric examples include:

► MW-206M sleeve style — 0.75–5mm, 0.25mm graduations, 16 blades
► MW-206MA sleeve style — 5.5–13mm, 0.5mm graduations, 16 blades
► MW-204M ring style — 0.75–5mm, 0.25mm graduations, 16 blades
► MW-204MA ring style — 5.5–13mm, 0.5mm graduations, 16 blades

Range comes first when choosing a radius gauge. A set covering small radii can't verify a profile beyond its specified blade range.

Metric vs Imperial Radius Gauges

Curves don't reveal their measurement system simply by looking at them.

The range includes both Metric & Imperial radius-gauge sets.

Imperial examples include:

► 1/32"–17/64" ranges
► 9/32"–33/64" ranges
► Sleeve-style gauges
► Ring-style gauges

Match the gauge system to the drawing, component or reference standard. Converting mentally between systems during inspection can introduce unnecessary uncertainty.

Ring-Style vs Sleeve-Style Radius Gauges

The same nominal radius can be packaged in different holder formats.

Both ring-style & sleeve-style sets provide individual radius profiles, but storage & blade presentation differ.

Consider:

► Workshop preference
► Frequency of use
► Available access
► Required radius range
► Metric or imperial system

The working profile remains the important feature. Choose the format that makes blade selection & positioning practical for the work being inspected.

Bore Gauges

Internal diameters can hide wear or variation that isn't obvious from the outside of a component.

The live collection includes 7 bore-gauge products.

Bore gauges can support suitable inspection around:

► Cylinders
► Housings
► Bushes
► Internal bores
► Machinery components
► Mechanical repairs

Bore inspection deserves more than one reading when wear is possible. Check the required method, measuring range & whether comparative measurements need to be taken across several positions.

Checking Bore Wear

A bore can change along its depth as well as across different directions.

Where appropriate, inspect:

► Near the opening
► Deeper within the bore
► Across different axes
► Known load areas
► Several repeatable positions

One measurement may hide taper or out-of-round wear. Multiple checks can provide a more useful picture before machining or replacement decisions are made.

Drill Gauges

A loose drill bit without a readable marking can turn a simple size check into unnecessary guesswork.

The collection includes 4 drill-gauge products.

Drill gauges can help identify suitable drill diameters by comparing them with known reference holes.

Useful applications include:

► Sorting workshop drills
► Checking unmarked bits
► Preparing drilling operations
► Tool-room organisation
► Maintenance work

A drill gauge identifies size rather than condition. Inspect the cutting edges, straightness & overall condition separately before returning an unknown drill to service.

Wire Gauges

Wire diameter can be awkward to judge reliably from appearance alone.

The live collection includes 2 wire-gauge products.

A suitable wire gauge can help identify known diameter or gauge references for compatible material.

Potential applications include:

► Workshop identification
► Fabrication
► Stock checking
► Wire sorting
► General engineering work

Confirm which gauge system the tool uses before interpreting the result. Gauge-number systems don't always correspond directly to a simple millimetre measurement.

Gauges for Fastener Identification

Finding a bolt in an unlabelled parts tray is only the beginning of identifying it correctly.

A practical fastener check may involve:

► Measuring diameter
► Checking length
► Identifying thread pitch
► Confirming thread standard
► Inspecting thread condition
► Checking head style
► Confirming grade where relevant

For supporting dimensional checks, Spear & Jackson | Precision Measurement Tools - Calipers complements screw-pitch gauges.

Once the specification is established, Nuts & Washers supports related replacement & assembly requirements.

For a broader overview of hardware identification, read the Fastener Guide.

Gauges for Automotive Work

Mechanical clearances often matter most in places where ordinary rulers have no practical role.

Suitable precision gauges can support checks around:

► Engine servicing
► Component gaps
► Mechanical adjustment
► Thread identification
► Radius comparison
► General workshop inspection

Always follow the equipment manufacturer's specified clearance or measurement procedure. A gauge can establish a dimension but doesn't determine what the correct service specification should be.

For broader workshop context, A Day With An Automotive Mechanic Peninsula looks at day-to-day automotive workshop work.

Gauges for Machinery Maintenance

Unexpected wear often reveals itself as a dimensional change before the entire component fails.

Inspection can involve:

► Clearances
► Threads
► Bores
► Profiles
► Replacement hardware
► Component fit
► Repeated dimensional checks

Record important findings when several components need comparing. Trends across repeated inspections can be more useful than isolated numbers remembered from one maintenance job.

For demanding industrial-maintenance environments, Quarry Crews Crusher Maintenance provides additional context.

Gauges vs Calipers

A direct dimensional reading isn't always the quickest way to answer an inspection question.

Think about the answer you need. If the question is “what pitch is this thread?”, use the appropriate pitch gauge. If the question is “what is this shaft diameter?”, a suitable caliper makes more sense.

Choosing Metric or Imperial Gauges

Using the same measurement system as the component or drawing reduces unnecessary conversion.

Choose Metric where:

► Dimensions are specified in millimetres
► Threads use Metric pitch
► Workshop drawings use Metric standards

Choose Imperial where:

► Dimensions are inch-based
► Legacy equipment uses imperial references
► Thread systems require an imperial gauge

Mixed workshops may need both systems. The collection includes individual Metric, Unified, Whitworth, American National & combination gauge configurations.

Checking a Gauge Before Use

Precision inspection starts with the condition of the reference surface itself.

Before use:

► Clean the gauge► Remove oil, swarf & debris
► Inspect blades or profiles
► Check for obvious deformation
► Confirm the correct range
► Select the correct blade or reference
► Clean the component contact area

A known reference becomes less useful when contamination sits between it & the workpiece. Clean contact can matter particularly with thin feeler blades or fine profile comparisons.

Using Gauges Without Forcing the Fit

The goal is to compare dimensions, not make the component conform to the gauge.

Avoid:

► Forcing feeler blades into clearances
► Bending pitch-gauge leaves against threads
► Dragging radius blades aggressively over finished surfaces
► Forcing reference holes over oversized components

Light controlled contact usually tells you more than excessive pressure. If the fit appears uncertain, reassess alignment & compare adjacent sizes.

Recording Inspection Results

A gauge can answer the immediate question, but recorded results become far more useful during repeated maintenance.

Record where useful:

► Gauge type
► Measured / matched size
► Component location
► Date
► Comparison with specification
► Changes from previous inspections

Consistent records can reveal wear or drift that isn't obvious from one workshop visit.

Protecting Precision Gauges

Thin blades, machined reference profiles & gauge edges deserve better treatment than being thrown loose under heavier hand tools.

Tool Storage & Organisation can help keep inspection equipment separated from striking tools, loose fasteners & abrasive workshop debris.

Useful habits include:

► Fold gauge leaves away after use
► Keep sets complete
► Protect machined edges
► Store tools dry
► Keep cases labelled
► Separate damaged gauges

Missing one blade from a multi-leaf set can leave a frustrating gap exactly where the next job needs it. Return every leaf or gauge to its correct storage position.

Caring for Precision Gauges

Inspection tools only remain useful while their reference surfaces remain trustworthy.

After use:

► Wipe away workshop residue
► Dry exposed steel surfaces
► Remove swarf
► Check blade movement
► Inspect edges & profiles
z► Store according to tool requirements

Treat gauges as measuring references rather than general hand tools. Avoid scraping, levering or marking with surfaces intended for inspection.

Expert Tips

Start With the Inspection Question

“How big is it?” & “does this profile match?” require different tools.

Choose the measuring principle before choosing the model.

Match Thread Standard Before Pitch

A blade fitting the spacing doesn't automatically prove the entire thread specification.

Confirm whether the component is Metric, Unified, Whitworth or another standard.

Don't Force Feeler Blades

A clearance check should use controlled contact rather than wedging the blade into place.

Compare neighbouring blade thicknesses where necessary.

Check Radii Against More Than One Blade

Two close profiles can look similar until both are compared carefully.

Use adjacent sizes to confirm the best match.

Inspect Worn Bores in Several Positions

Wear can create taper or out-of-round conditions rather than one uniform diameter change.

Repeat measurements across meaningful locations.

Keep Gauge Sets Complete

A missing reference blade creates a blind spot in the inspection range.

Return each component after use.

Use Calipers for Supporting Dimensions

Thread, radius & clearance gauges answer specialised questions while calipers fill in the surrounding dimensional picture.

Combine measuring methods where the repair requires more than one specification.