Bolt Torque Chart: Grade 2, 5, 8 and Metric

How tight should a bolt be? The usual answer is a torque that stretches the bolt to about three quarters of its proof load, the force it can carry without permanent stretch. This chart works that out for common inch bolts in SAE Grades 2, 5 and 8 and metric bolts in property classes 8.8, 10.9 and 12.9, for dry and lubricated threads. Every value is computed from the bolt’s stress area, the minimum proof strength in its standard and the standard torque-tension relation, so you can check or adjust any cell. A torque given by the maker of the machine, vehicle or fastener always takes precedence over a general chart.

Inch bolt torque chart (ft-lb)

Metric bolt torque chart (N·m)

Worked example: 1/2-13 Grade 8 and M10 class 8.8

A 1/2-13 UNC bolt has a tensile stress area of 0.1419 in². Grade 8 proof strength is 120,000 psi, so 75% of the proof load is 0.75 × 120,000 × 0.1419 = 12,771 lb of clamp force. With dry threads (K = 0.20) the torque to reach it is 0.20 × 0.5 × 12,771 ÷ 12 = 106 ft-lb; lubricated (K = 0.15) it drops to 80 ft-lb for the same clamp force.

An M10 x 1.5 bolt in class 8.8 has a stress area of 58.0 mm² and a proof stress of 580 MPa, so 75% of proof is 25.2 kN and the dry torque is 0.20 × 0.010 m × 25,225 N = 50 N·m (37 ft-lb).

Why lubrication matters so much

Most of the torque you apply goes into friction, under the head or nut and in the threads; only a small part stretches the bolt. Oil, anti-seize, wax or a slick plating cut that friction, so the same wrench torque produces much more clamp force. That is why the lubricated column is lower: torquing a lubricated bolt to a dry value can stretch it past its proof load or strip the threads. Use the column that matches your threads, and if a maker’s specification states “dry” or “oiled”, follow it exactly.

When this chart does not apply

• Wood and soft materials. Lag screws, carriage bolts and through-bolts in timber are limited by the wood crushing under the washer, not by the steel. Tighten until the washer is snug and just starts to bed in, and retighten after the wood dries. See our lag screw pilot hole chart.
• Tapped holes in aluminium, cast iron or plastic. The internal thread strips long before a steel bolt yields; use the equipment maker’s figure or much lower values, and enough thread engagement (see the tapped hole depth calculator).
• Gaskets, flanges, cylinder heads, wheels and anything safety-critical. These use specified torque sequences, torque-angle methods or new bolts each time. Follow the service manual.
• Stainless steel bolts. Stainless grades have different proof strengths and gall easily; use the supplier’s values and an anti-seize compound.

Frequently asked questions

How much torque for a 1/2 inch Grade 8 bolt?

About 106 ft-lb dry or 80 ft-lb lubricated for a 1/2-13 UNC bolt, giving 75% of the SAE J429 proof load. Use the maker’s figure if there is one.

What is the torque for an M10 bolt?

For class 8.8, about 50 N·m dry (37 ft-lb) or 38 N·m lubricated; class 10.9 takes about 43% more.

What is the difference between Grade 5 and Grade 8 bolts?

Grade 8 is a heat-treated alloy steel with a minimum proof strength of 120,000 psi against 85,000 psi for Grade 5, so it can be tightened about 40% harder. Grade 5 heads have three radial lines, Grade 8 six.

Should I oil bolts before torquing?

Only if the torque you are using is a lubricated value. Oil reduces friction, so a dry torque on an oiled bolt overtightens it.

Sources and method

Torques are computed, not copied: the stress area comes from the thread formula, the proof strength from the bolt standard, and the torque from T = K × D × F. Change K for your lubricant and the result scales directly.

1. SAE J429, Mechanical and Material Requirements for Externally Threaded Fasteners: minimum proof strength 55,000 psi (Grade 2, 1/4 to 3/4 in; 33,000 psi above), 85,000 psi (Grade 5, to 1 in; 74,000 psi above) and 120,000 psi (Grade 8), as published in fastener supplier tables.
2. ISO 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel: proof stress 580 MPa (class 8.8 to M16, 600 MPa above), 830 MPa (10.9) and 970 MPa (12.9), and the stress area formula.
3. Torque-tension short form T = K × D × F (for example, Bickford, An Introduction to the Design and Behavior of Bolted Joints); nut factor K about 0.20 for dry plain or zinc-plated steel and about 0.15 when lubricated, typical published values.
4. Stress areas computed on our UNC/UNF and metric thread charts (ASME B1.1, ISO 898-1 formulas).

More thread and fastener tools

• All thread and fastener charts
• UNC and UNF thread chart
• Metric thread pitch chart
• Tap drill chart (inch and metric)
• Clearance hole chart
• Nail size chart
• Wood screw size chart
• Lag screw pilot hole chart
• Bolt torque chart
• Wrench size chart
• Drill bit size chart
• Thread engagement chart
• Nail gun nail sizes by gauge
• Screw and nail size calculator
• Tap drill size calculator
• Clearance hole size calculator
• Tapped hole depth calculator

Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.