What torque should I use for an M10 bolt?

For a dry M10 bolt at the widely-cited K ~ 0.20 baseline, ISO 898-1 property-class guidance runs from roughly 18 N*m (class 4.6) up to about 72 N*m (class 12.9), with 42 N*m typical for class 8.8. Always check the bolt's head marking and the manufacturer's spec before relying on a generic table.

What does the K-factor mean?

K is an empirical torque coefficient that captures friction under the bolt head and in the threads for a given finish and lubrication state — roughly 0.20 for dry mild steel, lower when lubricated, and higher for some coatings such as black oxide.

Does Gibraltar use metric bolt grades?

Gibraltar follows UK/EU practice, so fasteners are specified to the ISO 898-1 metric property-class system (8.8, 10.9, 12.9). Legacy imperial hardware still appears on older British-sourced machinery, so check the head marking first.

Bolt Torque Calculator — Torque to Clamping Force | Construction Calculators

Bolt Torque Calculator: Tightening Torque from Clamping Force

Tightening a bolt to the correct torque keeps a joint clamped tightly enough to resist loosening under vibration and load, without overstressing the bolt, stripping its threads, or crushing a gasket. This calculator applies the standard torque-tension relationship, T = K x F x d, to convert between the torque applied with a wrench and the clamping (preload) force it actually produces, using a K-factor for the bolt's finish and lubrication state. It is a quick engineering estimate for common fasteners, not a substitute for a manufacturer's certified torque specification on a critical joint.

How to use the bolt torque calculator

Pick a solve direction: torque from clamping force, or clamping force from torque.
Choose a K-factor preset for the bolt's finish (dry mild steel, zinc-plated, black oxide, cadmium-plated) or enter a custom K, then enter the nominal bolt diameter.
Enter the clamping force (or applied torque), plus a lubricant preset if one is used — it reduces the effective K-factor automatically — to get the result.

The torque formula

The formula is T = K x F x d x (1 - l/100), where T is tightening torque, K is the empirical torque coefficient for the bolt's finish, F is the desired clamping force, d is the nominal bolt diameter, and l is the percentage torque reduction from any lubricant used.

Example: an M10 bolt (d = 0.01 m) needs 20,000 N of clamping force. With dry mild steel (K ~ 0.20) and no lubricant, T = 0.20 x 20,000 x 0.01 = 40 N*m. Switching to white grease (l ~ 35%) drops that to about 26 N*m for the same clamping force — lubrication changes the torque needed by more than a third.

Tips

Dry and lubricated K-factors differ by a wide margin — always match the K-factor and lubricant preset to the fastener's actual condition, since a dry value applied to a lubricated bolt over-tightens it for the same torque reading.

Where a manufacturer or a bolted-joint standard specifies a torque value directly, use that figure instead of a calculated one — this tool gives a general estimate, not a certified spec.

In Gibraltar, a standard steel bolt in common sizes typically retails for around £0.12 to £2.80 each depending on length, diameter, and property class.