Getting the torque right is one of the most important parts of assembling machinery, repairing vehicles and working with threaded fasteners. Tighten a bolt too loosely and it may work free under vibration. Apply too much force and you risk stretching the bolt beyond its limit, stripping the threads or damaging the component being secured.

A torque settings chart provides reference tightening values for bolts and screws based on their diameter, thread pitch, strength grade and friction conditions. Torque is usually measured in Newton metres (Nm) or foot-pounds (ft-lb). For metric steel bolts, common property classes include 8.8, 10.9 and 12.9, each with different mechanical strengths.

Whether you’re servicing a vehicle, maintaining workshop equipment or tackling a DIY project, this guide covers standard metric bolt torque settings, conversion tables, tightening techniques and the tools needed to achieve accurate results.

Important: The torque figures below are calculated general-purpose reference values, not universal manufacturer-approved settings or absolute maximum limits. Always follow the equipment or fastener manufacturer’s specification where one is provided, particularly for safety-critical components such as wheel fixings, brakes, steering assemblies, structural connections and electrical terminals.

Standard Metric Bolt Torque Settings Chart (Coarse Threads)

The following metric bolt torque chart covers common coarse-thread steel bolts in property classes 8.8, 10.9 and 12.9. Values are expressed in Newton metres (Nm) and assume clean, dry fasteners with a nominal friction factor.

Metric bolt torque settings – dry threads (Nm)

Indicative torque values based on approximately 70% of bolt proof load, a dry-thread nut factor of K = 0.20 and standard metric coarse pitches. Rounded reference values; not a substitute for joint-specific engineering requirements. MLC UK+1

How to Read the Metric Bolt Torque Chart

Start by identifying the diameter of the bolt. An M8 bolt, for example, has a nominal thread diameter of 8 mm, while an M12 bolt has a nominal diameter of 12 mm.

Next, check the bolt’s property class, which is normally stamped on its head. Find the corresponding column to obtain the reference tightening torque.

For example, the chart gives the following indicative dry-thread settings for an M10 bolt:

• Class 8.8: 49 Nm
• Class 10.9: 69 Nm
• Class 12.9: 81 Nm

The difference matters. A higher-strength bolt can generally withstand greater tensile loads, but that does not mean the surrounding joint, nut or tapped hole can safely accept a higher tightening torque.

Imagine replacing a bolt on a piece of workshop machinery. The original is an M10 class 8.8 fastener, but the replacement is class 12.9. Simply increasing the torque to match the stronger bolt could overload the threads in an aluminium housing or damage the component being clamped.

The correct setting must account for the complete assembly, not just the bolt.

Common Metric Bolt Sizes and Thread Pitches

Metric fasteners are identified by their nominal diameter and thread pitch. The pitch is the distance between adjacent thread crests, measured in millimetres.

For example, M10 × 1.5 describes a bolt with a 10 mm nominal diameter and a 1.5 mm thread pitch.

Fine-thread fasteners have a smaller thread pitch than their coarse-thread equivalents. As a result, the relationship between tightening torque and clamping force changes.

Never assume that an M10 × 1.25 fine-thread bolt uses exactly the same torque setting as an M10 × 1.5 coarse-thread bolt.

Metric Bolt Property Classes Explained: 4.6, 8.8, 10.9 and 12.9

The numbers stamped on a metric bolt head indicate its mechanical property class. These classifications are covered by ISO 898-1 for the applicable carbon steel and alloy steel fasteners.

The first number represents one-hundredth of the nominal tensile strength in megapascals (MPa). The second number, divided by ten, indicates the nominal ratio between yield strength and tensile strength for the familiar classes shown below.

Nominal property-class values for explanation. Actual specified minimum strengths and proof stresses depend on fastener diameter and the applicable ISO standard.

Class 4.6 – General-purpose, lower-strength fastening

Class 4.6 bolts are used in less demanding assemblies where high tensile strength is unnecessary. They may be suitable for certain brackets, light-duty fixtures and general fastening jobs, provided the design calls for this class.

Class 8.8 – Common engineering and automotive applications

Class 8.8 is widely used for steel structural components, mechanical assemblies and general workshop applications. It offers a useful balance of strength, availability and cost.

Class 10.9 – Higher-strength mechanical connections

Class 10.9 bolts are used where greater tensile strength is required. Depending on the design, applications may include automotive suspension assemblies, machinery and high-load mechanical joints.

Class 12.9 – High-strength engineering fasteners

Class 12.9 bolts provide particularly high tensile strength and are often used in specialised machinery, engineering equipment and socket-head screw applications.

An important distinction: bolt strength is not the same as joint strength. A class 12.9 bolt threaded into a relatively soft material may still strip the female threads if excessive preload is applied.

For more detail about metric fastener properties, see the official ISO 898-1 standard information. Note that ISO 898-1 specifies fastener mechanical properties; it does not prescribe universal tightening torque values. iso.org

Understanding Torque, Bolt Tension and Clamping Force

When you tighten a bolt, the aim is usually to generate enough clamping force to hold two or more components securely together.

Think about a bolt holding two steel plates. As the bolt is tightened, it stretches slightly, behaving much like a very stiff spring. That elastic stretch creates tension in the bolt and compresses the plates together.

This force is known as bolt preload.

Correct preload helps the joint resist movement and separation during normal operation. Insufficient preload may allow components to shift, while excessive preload can overstress the bolt or the materials being clamped.

The 90/10 Friction Principle

One of the most useful things to understand about torque tightening is that most of the effort applied to a fastener does not directly produce clamping force.

A commonly used engineering approximation suggests that:

Illustrative distribution of applied tightening torque

Conceptual approximation, not a fixed distribution for every fastener. Actual percentages vary with material, coatings, lubrication and joint geometry.

In other words, roughly 90% of the tightening effort can be consumed by friction, leaving only a relatively small proportion associated with stretching the fastener and establishing preload.

This helps explain why torque readings alone cannot guarantee an exact clamping force.

Two apparently identical bolts tightened to the same setting can produce different preload if one is clean and dry while the other has oil on its threads.

For general workshop work, a torque wrench provides a practical and repeatable method of controlling tightening. More demanding engineering applications may require additional methods of verifying bolt tension.

How Bolt Torque Is Calculated

A common simplified engineering relationship is:

Where:

• T = tightening torque in Nm
• K = dimensionless nut factor, representing the combined effects of friction and geometry
• F = desired bolt preload in Newtons (N)
• d = nominal bolt diameter in metres

Consider an M10 bolt with a desired preload of 25,000 N and a nut factor of 0.20.

Under these assumptions, a torque of approximately 50 Nm would be required.

Change the nut factor to 0.15, however, and the calculated torque becomes 37.5 Nm for the same desired preload.

That’s a substantial difference caused by friction alone. It also demonstrates why a standard torque settings chart should never be treated as universally correct for every finish, lubricant or joint construction.

Dry vs Lubricated Bolt Torque Settings

One of the easiest tightening mistakes is applying a dry-thread torque setting to a lubricated fastener.

Lubrication reduces friction between contacting surfaces. When that happens, the same tightening torque can generate significantly more bolt tension.

For example, a fastener tightened with oil or an anti-seize compound may reach a much higher preload than an otherwise identical dry fastener at the same torque setting.

How Much Should Torque Be Reduced for Lubricated Threads?

There is no universal percentage reduction that works for every fastener.

As an illustrative calculation, if a dry fastener has a nut factor of 0.20 and lubrication reduces it to 0.15, the required torque for the same preload falls by 25%.

Example: M10 bolt at 50 Nm dry torque

Dry, K = 0.20

50 Nm

Lubricated, K = 0.15

37.5 Nm

Illustration only. Do not automatically reduce a manufacturer’s specified torque by 25%; the original specification may already account for lubrication or coating.

Other factors that affect the relationship between torque and preload include:

• Zinc plating: Changes the surface characteristics of the fastener and may alter friction depending on any accompanying treatment.
• Anti-seize compounds: Can substantially change the friction characteristics of threaded connections.
• Thread-locking compounds: May affect assembly friction and can have specific application requirements.
• Corrosion and contamination: Dirt, damaged threads and rust can increase friction and make torque readings less representative of preload.
• Washers and bearing surfaces: Different materials, surface finishes and washer arrangements can influence the torque required.

A common workshop example is a bolt that has been cleaned and lightly oiled during maintenance. If the original specification assumed a dry fastener, simply tightening the lubricated bolt to the old setting may create excessive tension.

Before reaching for the torque wrench, establish whether the quoted setting assumes dry, lubricated, coated or otherwise treated threads.

Should You Lubricate Every Bolt Before Tightening?

No. Lubrication should only be applied when specified or permitted by the manufacturer or engineering procedure.

Some fasteners are intended to be installed dry. Others require a defined lubricant, pre-applied coating or thread-locking compound.

Wheel fixings are a particularly important example. Vehicle manufacturers may specify clean, dry threads, and adding lubricant without authorisation can change the clamping force achieved at the prescribed torque.

The safest rule is straightforward: match the condition of the threads to the condition assumed by the tightening specification.

Torque Conversion Chart: Nm to ft-lb and in-lb

Torque specifications are not always expressed in the same units. UK workshop manuals generally use Newton metres (Nm), while American service documentation often uses foot-pounds (ft-lb) or inch-pounds (in-lb).

The following torque conversion chart provides quick reference values for commonly used settings.

Torque Conversion Formulas

Use these formulas when converting a setting from a workshop manual.

Newton metres to foot-pounds:

Foot-pounds to Newton metres:

Newton metres to inch-pounds:

For example, if a vehicle service manual specifies a tightening torque of 90 Nm:

A setting of 90 Nm is therefore approximately 66.4 ft-lb.

Interactive Torque Converter

Unit conversion only. This does not calculate the appropriate tightening torque for a component.

Application-Specific Torque Settings

General bolt torque charts are useful for engineering reference, but many applications require their own tightening specifications.

Automotive components, electrical terminals and precision bicycle parts are good examples. Their torque requirements depend on much more than the diameter and strength of an individual fastener.

Automotive Torque Settings

Automotive repairs involve everything from relatively small engine-cover bolts to heavily loaded suspension and drivetrain components.

Common applications requiring controlled tightening include wheel bolts, wheel nuts, cylinder heads, brake components, spark plugs, suspension fixings and engine mounting bolts.

When servicing a vehicle, use the manufacturer’s workshop instructions rather than selecting a value from a generic metric bolt chart.

An M12 wheel bolt, for example, may require a different tightening procedure from an M12 bolt securing a steel bracket. The wheel fixing’s design, seat profile, clamped materials and operating loads all influence the specification.

Some automotive fasteners also require torque-angle tightening.

A manufacturer might specify an initial torque followed by a further angular rotation. This procedure must be followed exactly, including any instruction to use new bolts.

Workshop tip: When tightening wheels, use a suitable torque wrench for the final tightening stage and follow the vehicle manufacturer’s sequence. An impact wrench is useful for removal and initial assembly where appropriate, but it should not replace the specified final tightening procedure.

Electrical Consumer Units and MCB Torque Settings

Electrical terminal torque is especially important because insufficient clamping can contribute to loose connections, increased resistance and overheating. Excessive tightening can also damage terminals or conductors.

Unlike ordinary structural bolts, miniature circuit breakers (MCBs) often use comparatively low tightening torques.

For example, Schneider Electric documentation provides the following specifications for particular products:

These figures are examples from specific product documentation, not universal settings for all consumer units or MCBs. ckm-content.se.com+1

Always check the exact manufacturer’s terminal torque, conductor requirements and installation instructions. Work inside consumer units should be carried out by suitably competent personnel following the applicable electrical safety procedures.

For controlled low-torque fastening, Jawel Tools offers a range of torque screwdrivers, including products designed for precision adjustment.

Bicycle Torque Settings

Modern bicycles often combine lightweight aluminium components, high-strength steel fasteners and carbon-fibre parts. Incorrect tightening can damage components, particularly where thin-walled tubes or lightweight clamps are involved.

The following ranges illustrate why different tools may be needed for different bicycle maintenance tasks.

These are broad examples only. Actual manufacturer specifications can fall outside these ranges, and some components require different installation methods.

A stem faceplate is a good example of why bolt torque alone does not tell the whole story. Tightening one bolt fully before the others may produce uneven clamp pressure, even if every bolt eventually reaches the specified value.

Follow the prescribed tightening sequence and any stated gap requirements. On carbon components, use only the assembly compounds and procedures approved by the manufacturer.

Choosing the Right Torque Wrench

An accurate torque setting is only useful when you have the correct tool to apply it.

Torque wrenches are available in different designs, drive sizes and measurement ranges. Choosing the right one depends primarily on the tightening torque required, the available working space and how frequently the tool will be used.

Micrometer Torque Wrenches

Micrometer or click-type torque wrenches are widely used in automotive workshops, engineering and general mechanical servicing.

The operator adjusts the handle to the required value and applies force until the wrench gives its designated click or release indication.

These tools are particularly useful for repetitive workshop tasks where consistent tightening is needed.

For example, Jawel Tools stocks the Sealey Premier Calibrated Micrometer Torque Wrench 1/2″Sq Drive (AK624), suitable for consideration when selecting workshop torque equipment. Check the individual product’s working range against the fasteners you need to tighten.

Digital Torque Wrenches

Digital models provide an electronic torque display and may include audible alerts, visual indications or additional measurement features.

Some models also support peak-hold or torque-angle functions, depending on their specification.

These can be useful for specialist mechanical work and situations where readings need to be monitored closely.

Torque Screwdrivers

For smaller fasteners and low tightening values, a torque screwdriver is often more suitable than a conventional torque wrench.

These are particularly useful for suitable electrical terminals, instrumentation, precision assemblies and delicate mechanical components.

A large automotive torque wrench is unlikely to be appropriate for a terminal requiring just 2 Nm.

Which Drive Size Should You Choose?

Drive size does not determine the tool’s torque range by itself. Always check the manufacturer’s rated minimum and maximum values.

At Jawel Tools, you can explore the appropriate ranges:

• 1/4″ Square Drive Torque Wrenches
• 3/8″ Square Drive Torque Wrenches
• 1/2″ Square Drive Torque Wrenches
• 3/4″ Square Drive Torque Wrenches

How to Tighten a Bolt Correctly Using a Torque Wrench

Knowing the specified torque is only part of the job. The way you prepare the fastener, position the tool and apply force can affect the final result.

1 Identify the correct specification

Check the bolt size, property class, thread condition and equipment manufacturer’s instructions. Confirm whether the required setting is in Nm, ft-lb or another unit.

2 Inspect the fastener and threads

Look for corrosion, cross-threading, damaged threads or evidence of previous overstretching. Replace damaged or single-use fasteners as required by the manufacturer.

3 Select the correct socket and wrench

Use a socket that fits securely and a torque wrench whose rated operating range comfortably covers the specified tightening value.

4 Start the fastener by hand

Engage the threads carefully before applying significant force. A fastener that resists immediately may be misaligned or cross-threaded.

5 Follow the tightening sequence

Where several bolts clamp the same component, follow the manufacturer’s specified order and stages. This is particularly important for flanges, covers, wheel assemblies and other multi-bolt joints.

6 Apply smooth, controlled force

Grip the wrench at its designated handle position and pull steadily. Stop at the prescribed indication rather than continuing to force the handle.

7 Complete the prescribed procedure

Carry out any required angle-tightening, inspection or recheck instructions. Reset and store the torque tool according to its manufacturer’s guidance.

Common Torque Tightening Mistakes

Even experienced mechanics can run into problems when tightening procedures become routine.

Using the wrong units: Confusing Nm and ft-lb can produce a substantial error. A setting of 100 ft-lb is approximately 135.6 Nm, not 100 Nm.

Using a wrench outside its rated range: A large wrench intended for heavy fasteners should not be relied upon for a small fastener requiring minimal torque.

Continuing after the click: On click-type tools, continuing to pull after the setting is reached can result in overtightening.

Adding an extension to the handle: Improvised handle extensions can change the applied force and potentially overload the wrench. Use only accessories and operating methods approved for the tool.

Ignoring lubrication: Applying a dry-thread torque setting to lubricated threads can create excessive preload.

Assuming all bolts of the same diameter use the same setting: Bolt strength, thread pitch and joint construction all matter.

Torque Wrench Calibration and Maintenance

A torque wrench is a measuring instrument as well as a tightening tool. Its readings should be reliable enough for the work being carried out.

Over time, mechanical wear, incorrect handling or damage may affect its performance.

How Often Should a Torque Wrench Be Calibrated?

For professional workshops, an annual calibration interval is commonly used as a starting point. Some manufacturers specify intervals based on time, number of operating cycles or usage conditions.

The appropriate frequency depends on how regularly the wrench is used, the accuracy required and the manufacturer’s instructions.

ISO 6789-2:2017 establishes requirements for the calibration of hand torque tools and the assessment of measurement uncertainty. It should not be interpreted as a universal requirement to calibrate every torque wrench annually. iso.org

A torque wrench should also be checked following suspected damage, particularly if it has been dropped or subjected to an excessive load.

Maintaining Your Torque Wrench

Keep the tool clean and store it in its protective case when not in use. Avoid exposing it unnecessarily to moisture, dirt and workshop chemicals.

For micrometer-style wrenches, follow the manufacturer’s storage-setting instructions. Some models should be returned to their lowest marked setting, while other designs have different requirements.

Never use a precision torque wrench as a general breaker bar to loosen seized bolts unless the tool has been specifically designed and approved for that purpose.

Frequently Asked Questions About Torque Settings

What Is the Correct Torque Setting for an M8 Bolt?

For a standard metric coarse-thread M8 bolt, an indicative dry-thread tightening value is approximately 25 Nm for property class 8.8, 35 Nm for class 10.9 and 41 Nm for class 12.9, using the reference chart above.

The actual setting must be confirmed against the joint manufacturer’s requirements.

What Is the Torque Setting for an M10 Bolt?

For general-purpose dry-thread reference conditions, an M10 coarse-thread bolt has indicative settings of 49 Nm for class 8.8, 69 Nm for class 10.9 and 81 Nm for class 12.9.

These figures should not be substituted for manufacturer-specified tightening values on vehicle or machinery components.

Is a Higher Bolt Grade Always Better?

No. Higher-strength bolts can withstand greater tensile loads, but the surrounding joint may not be designed for higher preload.

Replacing a class 8.8 bolt with a class 12.9 fastener does not automatically improve the assembly. The correct fastener must match the engineering requirements of the component.

Should Oiled Bolts Be Tightened More or Less?

Lubricated fasteners generally require less torque to achieve the same preload, assuming the lubricant reduces friction.

The amount depends on the lubricant, coating, fastener geometry and joint. Do not apply an arbitrary percentage reduction to a manufacturer’s specified torque.

Can I Use an Impact Wrench Instead of a Torque Wrench?

An impact wrench can help remove and install suitable fasteners, but it is not normally an acceptable substitute for accurate final torque tightening.

Use a correctly rated torque wrench or another manufacturer-approved controlled-tightening method for the final stage.

Do Torque Wrenches Need Calibrating?

Yes, torque wrenches used for controlled tightening should be checked and calibrated according to their manufacturer’s instructions and the requirements of the work.

Professional workshops should establish a documented inspection and calibration schedule appropriate to tool usage and risk.

Get the Right Torque, Every Time

Correct tightening protects far more than the bolt itself. It helps maintain secure mechanical connections, prevents unnecessary component damage and makes repairs more reliable.

A standard torque settings chart provides a useful starting point for identifying the relationship between bolt size, strength and tightening force. The important part is knowing when that reference figure is appropriate and when a specific manufacturer’s procedure must take priority.

Whether you’re maintaining a vehicle, assembling machinery or building a home workshop, a quality torque wrench and the correct sockets are valuable additions to your toolkit.

With over 50 years of experience supplying tools and workshop equipment, Jawel Tools offers a wide selection of equipment for professional tradespeople, mechanics and DIY enthusiasts.

Explore our complete range of torque wrenches and find the equipment suited to your next job.