Bolt Torque Chart: Recommended Torque Values for Common Bolt Grades

Most people who search for a bolt torque chart already have a wrench in one hand and a bolt in the other. They don’t want a lecture. They want a number, so here it is: a grade 8.8 M10 bolt takes about 50 Nm when the thread is dry and about 38 Nm when it is lightly lubricated. That gap of roughly a quarter is the whole reason no single figure works everywhere, because most of the bolt tightening torque you apply with a wrench goes into friction rather than into stretching the bolt. So treat any chart, this one included, as a sensible place to start, and follow the joint specification if you have been given one.

Unifit Fastener puts this guide together for engineers, buyers and maintenance teams who want clear bolt torque specifications instead of a sales pitch. A torque chart for bolts is only useful when you can see how the numbers were built, so every table states its assumptions. Inside you will find metric values in Nm, inch values in ft lb for SAE Grade 5, Grade 8 and ASTM A193 B7 bolts, guidance for stainless steel, the formula behind every value and a way to work out your own.

Need certified bolts to match the grade you are tightening? Send us your size, grade and standard and we will confirm availability and lead time.

What Is Bolt Torque?

Bolt torque is the turning force applied to a bolt or nut with a wrench to tighten a joint. It is usually measured in Nm, ft lb or in lb. However, the torque applied to a bolt does not directly represent the tension created in it. A significant part of the applied torque is used to overcome friction in the threads and beneath the bolt head or nut. The rest of the force stretches the bolt and produces the clamp load needed to hold the joint together.

This is why there is no single torque value that works for every bolt. The required tightening torque can change with the bolt size, grade, thread condition, lubrication, surface coating and required clamp load. For example, a dry bolt and a lubricated bolt of the same size and grade may need different torque values. The torque charts below are based on specific assumptions, so use the value that matches your bolt and tightening conditions rather than treating any one figure as a universal setting.

Metric Torque Values in Nm for Grades 8.8, 10.9 and 12.9

This metric bolt torque chart covers 8.8, 10.9 and 12.9 bolt torque for coarse thread sizes from M6 to M30. Values follow the ISO 898 part 1 property classes and are in Nm, so it works as a bolt torque chart in Nm for most projects outside North America. For each grade, read clamp force in kN first, then dry torque, then lubricated torque. The values apply to any bolt of these property classes, including our  Grade 8.8 hex bolts and our Grade 12.9 bolts.

Assumptions: ISO metric coarse thread, clamp load 75 per cent of proof load, K of 0.20 dry and 0.15 lightly lubricated, T = K × d × F with d in metres and F in newtons. Proof stress is 580 MPa for Grade 8.8 up to M16 and 600 MPa above, 830 MPa for Grade 10.9 and 970 MPa for Grade 12.9. Tensile stress areas are taken from ISO 898 (M10 is 58.0 mm² and M12 is 84.3 mm²). Rounded to the nearest 1 Nm.

Inch Torque Values in ft lb for SAE Grade 5, Grade 8 and ASTM A193 B7

For inch series bolts, this grade 8 bolt torque chart and grade 5 bolt torque chart give clamp load in pounds and tightening torque in ft lb for UNC coarse threads from 1/4 to 1 1/2 inch. ASTM A193 B7 is included because it is the standard flange stud material. Read the dry column for clean, as received threads and the lubricated column for lightly lubricated ones.

Assumptions: UNC coarse thread, clamp load 75 per cent of proof load, K of 0.20 dry and 0.15 lightly lubricated, T = K × D × P divided by 12. Proof stress is 85 ksi for Grade 5 up to 1 inch and 74 ksi above, and 120 ksi for Grade 8. A193 B7 lists yield rather than proof, so its 105 ksi minimum yield is the reference stress. Stress area is 0.7854 × (D minus 0.9743 divided by n) squared, with n threads per inch. Rounded to the nearest 1 ft lb. SAE Grade 5 and 8 are not made above 1 1/2 inches.

Stainless Steel Bolt Torque: A2 70, A4 80 and ASTM A193 B8

Stainless steel bolt torque needs its own thinking, so a carbon steel chart cannot be reused for it. Stainless bolts have lower yield strength than grade 8.8 and above, higher thread friction, and a habit of galling. Galling is when thread surfaces cold weld and tear, and it can seize a nut long before you reach the number on a chart. Lubricant matters even more here, and it lowers K, so the wrench reading for the same clamp load drops. Slow, steady tightening helps too, because speed builds heat and friction. Use the reference strengths below in the same formula, take K from your lubricant supplier and confirm the result against the joint specification. For ASTM A193 Grade B8 material, see our ASTM A193 Grade B8 fasteners.

Reference strengths for stainless bolting

Class 2 strain hardened B8 strength depends on diameter, so check ASTM A193 for the size you are using.

We leave out a stainless torque table on purpose. Published values swing widely with alloy, finish, lubricant and mating material, and a guessed number is worse than none. The same goes for nickel alloy fasteners and other high-alloy bolting: use the method, then confirm with an engineer.

How to Choose the Right Torque Value, Step by Step 

Five steps get you to the right number without guesswork.

1. Identify the grade. Read the head marking or check the mill test certificate. A wrong grade means the wrong table, so do not guess from appearance.
2. Confirm size and thread pitch. Check whether the thread is coarse or fine. The tables here cover coarse threads only.
3. Decide the thread condition. Is it dry, lightly lubricated, plated or galvanised? If it is not dry, do not use the dry column.
4. Read the value from the right table. Match the standard: ISO 898 part 1 for metric, SAE J429 for Grade 5 and Grade 8, ASTM A193 for B7.
5. Tighten in stages with a calibrated torque wrench, then check. Bring the bolt up in steps rather than one hard pull, then confirm the final value.

How Bolt Torque Values Are Calculated and Why Charts Differ

Every value here comes from one short formula, so you can check it yourself. For metric bolts, T = K × d × F, where T is torque in Nm, K is the friction (nut) factor, d is the nominal diameter in metres and F is the clamp load in newtons. For inch bolts, T = K × D × P divided by 12, with D in inches, P in pounds and T in ft lb. Clamp load is 75 per cent of proof load, which is proof stress times tensile stress area. Proof stresses come from the property class standards, and our guide to fastener standards and specifications explains how they fit together.

Worked example, metric. M10 grade 8.8 has a proof stress of 580 MPa and a stress area of 58 mm², so the proof load is 33.6 kN and the clamp load at 75 per cent is 25.2 kN (25,230 N). With K of 0.20 and d of 0.010 m, T = 0.20 × 0.010 × 25,230 = 50.5, so about 50 Nm.

Worked example, inch. A 1/2 inch 13 UNC Grade 5 bolt has a stress area of 0.1419 in² and a proof stress of 85,000 psi, so the proof load is about 12,062 lb. At 75 per cent, P is 9,046 lb. With K of 0.20, T = 0.20 × 0.5 × 9,046 divided by 12 = 75.4, so about 75 ft lb.

Friction (K) values by thread condition

Real K varies with finish, lubricant and how many times the parts have been used. The charts in this guide use only 0.20 and 0.15. Real K is confirmed by torque and clamp force testing to ISO 16047, and it can change with the fastener finish, lubricant and number of times the parts have been used.

Why do other charts show different numbers? Published charts can disagree by 10 to 30 per cent because some take clamp load as 70 per cent of proof, some 75 and some 85, they use different K values, and they assume different lubricants. Run the M10 grade 8.8 example at 85 per cent, and the dry value becomes about 57 Nm instead of 50 Nm. Neither chart is wrong as long as it states its assumptions. This one does.

Torque is only a proxy for tension. A widely quoted rule of thumb is that about 90 per cent of bolt tightening torque goes into overcoming friction under the head and in the threads, while only a small share stretches the bolt and creates clamp load. This means that even small changes in friction can significantly affect the resulting clamp load. For critical joints, engineers use tension indicating washers, torque turn tightening or hydraulic tensioning instead. 

What Affects Bolt Torque: Lubrication, Finish, Thread and Joint

The number on a chart is only right for the conditions it assumes. These are the things that move it.

• Lubrication and anti-seize: less friction means more clamp load for the same torque.
• Plating and galvanising: coatings change K, upward with hot dip galvanising and downward with waxed or PTFE finishes. See our guide to fastener coatings.
• Coarse versus fine thread: a fine thread has a larger stress area, so a coarse value does not carry over.
• Nut and washer grade: a soft nut or washer embeds and relaxes. Match the nut to the bolt and use the washer the joint calls for, such as DIN 126 plain washers.
• Joint stiffness and gaskets: a gasket or soft joint compresses, and the preload drops.
• New versus reused bolts: used threads have different friction, and a stretched bolt holds less.
• Temperature: heat changes friction, relaxes the joint and lowers strength.

One rule to remember: never apply a dry value to a lubricated bolt. With K at 0.15 instead of 0.20, a dry value lifts the clamp load by about a third, so a 75 per cent target becomes close to 100 per cent of proof load. That can overtighten the bolt, damage the thread or yield the bolt.

Bolt Grades and Markings Explained

Most wrong torque values start with a misread grade. On metric bolts the head shows the property class, such as 8.8 or 10.9. The first number times 100 gives the nominal tensile strength in MPa, and the second is the yield-to-tensile ratio in tenths, so 8.8 means about 800 MPa tensile with yield at 80 per cent of that. On SAE bolts, radial lines show the grade: three for Grade 5 and six for Grade 8. ASTM A193 B7 carries a B7 mark. Grade 8 (inch) and 8.8 (metric) belong to different systems and are not the same strength.

B7 is a chromium molybdenum alloy steel, commonly made from grades such as AISI 4140 fasteners. For the full strength comparison and selection advice, read our guide to grade 8.8 vs 10.9 vs 12.9 bolts, or see our overview of bolt grades. New to the parts themselves? Start with the types of nuts, bolts and screws.

Tightening Sequence and Method, Including Flanges

The right bolt-tightening torque applied in the wrong order still gives an uneven joint.

• Tighten in a cross (star) pattern so the load builds evenly across the joint.
• Work in stages, for example, 30 per cent, then 60 per cent, then 100 per cent of the target.
• Finish with a final pass in circular order to catch any bolt that relaxed as its neighbours came up.
• Use a calibrated torque wrench and check it regularly. ISO 6789 covers torque tool calibration.

Flanged and gasketed joints are a special case. Gasket stress sets the target, not a bolt chart, so use the gasket maker’s guidance and the bolted joint procedure in ASME PCC 1, and never lift a flange value from this page. Flange work often uses stud bolts and threaded rods in A193 B7 or B8, and our guide to ASTM A193 Grade B7, B8 and B8M fasteners covers the nut pairings. For critical joints, torque turn tightening, direct tension indicators and hydraulic tensioning are alternatives to plain torque control. 

Structural bolts are a separate case. For ASTM A325 and A490 bolts, now published under ASTM F3125, the RCSC specification sets a minimum pretension for each size and accepts installation methods such as turn of nut, calibrated wrench, twist off bolts and direct tension indicators. Acceptance is based on tension, not on a value from a general torque chart.

Common Mistakes When Tightening Bolts

• Applying dry values to lubricated bolts. It is the most common mistake and the one that does the most damage.
• Using coarse thread values on fine thread bolts. The stress area is different, so the torque is too.
• Reusing yielded bolts. A bolt that has stretched will not hold the clamp load it did when new.
• Trusting an uncalibrated wrench. A tool that has drifted quietly puts the wrong load into every bolt it touches.
• Mixing grades. A 12.9 bolt with a weak nut or a soft washer is only as strong as its weakest part.
• Torquing the wrong part. Where a joint has a bolt and a nut, tighten the nut and hold the head when you can, because friction under the turning part sets the result. 

Torque Unit Conversion: Nm, ft lb, in lb and kgf m

Mixed unit projects are common, so here is a quick reference.

Table 6: Torque unit conversion

Three quick examples: 50 Nm × 0.7376 is about 36.9 ft lb. 75 ft lb × 1.3558 is about 101.7 Nm. 120 in lb × 0.1130 is about 13.6 Nm.

Bolt Torque Calculator: Work Out Your Own Value

If your bolt sits between the rows, or your finish is not dry or lightly lubricated, run the numbers yourself. This is the bolt torque calculator logic behind the tables, in four steps.

1. Find the proof load: proof stress times tensile stress area.
2. Take 75 per cent of it as the target clamp load, F or P.
3. Choose K for your thread condition from Table 4.
4. Multiply: T = K × d × F for Nm, or T = K × D × P divided by 12 for ft lb.

Your answer should land close to the tables when K is 0.20 or 0.15. Disclaimer: the result estimates tension and is not a guarantee, so follow the joint specification.

Not sure which grade or finish your joint needs? Send us your drawing or specification and our team will help you match grade, finish and standard.

Frequently Asked Questions

Related Reading

ISO Fastener Standards and Types of Stainless Steel Fasteners, Grades and Applications from the Unifit Fastener blog.