Metric Bolt Torque Chart M6-M24: Class 8.8, 10.9 & 12.9

Quick answer

For a clean, dry, coarse-thread metric bolt, a practical reference torque is about 25 N·m for M8 class 8.8, 72 N·m for M10 class 10.9, and 147 N·m for M12 class 12.9. These are calculated starting values, not universal assembly specifications. Lubrication, zinc coating, anti-seize, prevailing-torque nuts, joint materials and manufacturer requirements can change the torque needed for the same clamp load.

Metric bolt torque chart: M6-M24

The chart below uses coarse metric threads and shows approximate tightening torque in N·m. Each cell is Dry / Lubricated.

Size and coarse pitch | Class 8.8 | Class 10.9 | Class 12.9 M6 x 1.0 | 10 / 8 | 15 / 11 | 18 / 13 M8 x 1.25 | 25 / 19 | 36 / 27 | 43 / 32 M10 x 1.5 | 50 / 38 | 72 / 54 | 84 / 63 M12 x 1.75 | 88 / 66 | 126 / 94 | 147 / 110 M14 x 2.0 | 140 / 105 | 200 / 150 | 234 / 176 M16 x 2.0 | 219 / 164 | 313 / 235 | 365 / 274 M18 x 2.5 | 301 / 226 | 430 / 323 | 503 / 377 M20 x 2.5 | 426 / 320 | 610 / 458 | 713 / 535 M22 x 2.5 | 580 / 435 | 830 / 622 | 970 / 727 M24 x 3.0 | 737 / 553 | 1,055 / 791 | 1,233 / 925

How the reference values were calculated

The table uses the common torque-preload relationship T = K x D x F. T is tightening torque, K is the nut factor, D is nominal bolt diameter and F is target preload. The calculation assumes a target preload of 75% of proof load, ISO metric coarse-thread tensile stress areas, a nut factor of 0.20 for clean dry steel and 0.15 for a controlled lubricated condition. Values are rounded to practical whole N·m.

Property classes 8.8, 10.9 and 12.9 follow ISO 898-1 strength conventions for carbon and alloy steel fasteners. This chart does not apply to A2-70 or A4-80 stainless steel merely because the diameter is the same. Stainless assemblies have different proof properties and a higher risk of thread galling.

Why two torque charts can disagree

Torque is only an indirect method of creating bolt preload. Bolt Science notes that most applied torque is consumed by friction in the threads and under the rotating bearing face; only a small portion stretches the bolt. A change in lubricant, coating, washer, surface roughness or tightening method can therefore create a large change in clamp load even when the torque wrench shows the same number.

Published charts may use different target preload percentages, proof strengths and nut factors. A table using K = 0.18 will show a lower dry torque than one using K = 0.20. Neither number is meaningful unless its assumptions match the actual joint.

Dry, lubricated and coated fasteners

Never apply a dry torque value automatically to an oiled or anti-seize-coated fastener. Lower friction produces more preload at the same wrench setting and can stretch or break the bolt. The lubricated column above uses a 25% reduction as a controlled comparison, but the lubricant supplier or joint engineer should provide the final factor.

Zinc plating, hot-dip galvanizing, wax, phosphate coating and thread-locking compounds each create different friction conditions. Hot-dip galvanized assemblies may also require oversize-tapped nuts and coating-compatible mating parts. Ask the supplier for the coating system and torque or friction data as one assembly rather than selecting a bolt, nut and torque value independently.

When not to use a generic torque chart

Do not use this table as the final specification for torque-to-yield bolts, structural preloaded bolting, pressure-containing joints, critical lifting equipment, rotating machinery governed by an OEM procedure, aluminum or plastic internal threads, gasketed joints, prevailing-torque lock nuts, damaged threads or any assembly with a validated tightening procedure.

For safety-critical joints, the drawing, equipment manual, applicable construction code or engineer-approved tightening procedure takes precedence. Where clamp load matters, torque-angle, direct tension indicators, ultrasonic measurement or assembly testing may provide better control than torque alone.

How buyers should specify bolt torque in an RFQ

Provide the bolt standard and dimensions, property class, thread pitch, material, coating, lubricant or thread-locker, mating nut and washer, joint materials, target preload or approved torque, tightening method, reuse policy, inspection method and required documents. Include the drawing or application standard when available.

For example, "ISO 4017 M10 x 50, class 10.9, zinc plated, ISO 4032 nut and washer, controlled lubricated assembly, target tightening torque subject to supplier friction data" is much safer than writing only "M10 bolt, 72 N·m."

Practical selection workflow

First identify the exact bolt diameter, pitch and property class. Second confirm whether the threads and bearing face are dry, plated, waxed, oiled or treated with anti-seize. Third check the joint drawing, OEM manual and applicable standard for a specified tightening method. Fourth confirm that the nut, washer and tapped material can carry the intended preload. Finally validate the torque on the actual production assembly before releasing a critical process.

Sources and technical basis

ISO 898-1 provides mechanical property requirements for carbon and alloy steel fasteners. Bolt Science technical references explain torque-preload scatter and the dominant effect of thread and bearing-face friction. Portland Bolt's torque guidance likewise describes published torque values as starting estimates and recommends testing under actual joint conditions. Always verify the current official standard, project specification and supplier data before production.

Need a quotation?

Send SavinIndustry the bolt standard, size, property class, finish, quantity, mating parts and application conditions. We can help turn the requirement into a clearer fastener RFQ and flag missing assembly details before quotation.