Bolt Torque Settings Calculator

For a grade 8.8 M6 bolt with clean, lightly oiled threads tightening into steel, the recommended torque is approximately 9.5 Nm. For grade 10.9 M6, use approximately 14 Nm. For grade 12.9 M6, use approximately 16 Nm. M6 bolts are common on hydraulic valve bodies, electrical brackets, and small cover plates on fleet and plant machinery.

For a grade 8.8 M8 bolt with lightly oiled threads, the recommended torque is approximately 23 Nm. For grade 10.9 M8, use approximately 34 Nm. For grade 12.9 M8, use approximately 40 Nm. If the bolt is dry, increase by 25%. M8 bolts are found on linkage brackets, guard fixings, pump mounting, and cab fittings throughout fleet and plant machinery.

For a grade 8.8 M10 bolt with lightly oiled threads, the recommended torque is approximately 46 Nm. For grade 10.9 M10, use approximately 68 Nm. For grade 12.9 M10, use approximately 79 Nm. M10 is a very common size on frame joints, hydraulic block mounting, and chassis brackets.

For a grade 8.8 M12 bolt with clean, lightly oiled threads tightening into steel, the recommended torque is approximately 79 Nm. For grade 10.9 M12, use approximately 115 Nm. For grade 12.9 M12, use approximately 135 Nm. M12 is one of the most common sizes on UK fleet and plant machinery — three-point linkage pins, drawbar bolts, and gearbox mounting. If using copper anti-seize, reduce these figures by approximately 20%.

For a grade 8.8 M16 bolt with lightly oiled threads, the recommended torque is approximately 195 Nm. For grade 10.9 M16, use approximately 280 Nm. For grade 12.9 M16, use approximately 330 Nm. M16 is common on main frame bolts, PTO/driveline guard fixings, and cab mount bolts. A 1/2" drive torque wrench typically reaches 340 Nm — just enough for an M16 grade 10.9.

For a grade 8.8 M20 bolt with lightly oiled threads, the recommended torque is approximately 385 Nm. For grade 10.9 M20, use approximately 560 Nm. For grade 12.9 M20, use approximately 650 Nm. At this size a 3/4" drive torque wrench or a torque multiplier with a 1/2" wrench is needed for accurate results.

The numbers refer to the property class (strength) of the bolt per ISO 898-1. Grade 8.8 is medium-strength carbon steel — the most common general-purpose bolt on fleet and plant machinery. Grade 10.9 is high-strength alloy steel, used in structural joints, flanges and precision machinery. Grade 12.9 is the highest common grade, maximum tensile strength, usually with a black oxide finish. The grade is stamped on the bolt head. Never substitute a lower grade for a higher grade without recalculating the required torque — the bolt may fail in service.

Yes — significantly. Copper anti-seize (Copaslip) reduces the friction coefficient, so the same torque produces more clamping force than a dry or oiled bolt. If you apply anti-seize and use the standard oiled torque figure, you risk over-stressing the bolt and potentially stripping threads or fracturing the bolt. Reduce the torque by approximately 20% compared to a lightly oiled condition, or by about 36% compared to a dry condition. The calculator above handles this automatically.

For general workshop use you need at minimum a 3/8" drive torque wrench (5–80 Nm) for smaller fasteners and a 1/2" drive torque wrench (40–340 Nm) covering most M8–M20 bolts. For large fasteners like M24+ or driveline flanges, a 3/4" drive torque wrench (100–800 Nm) or a torque multiplier used with a 1/2" drive wrench gives better accuracy at high values. Cheap click-type torque wrenches drift over time — calibrate or replace every 2–3 years.

Wheel nut torque must always come from the manufacturer's service manual — it varies significantly by make, model, rim size, and stud specification. Typical values range from 390 Nm to 680 Nm on agricultural and plant machinery, and higher again on HGVs, but this is only a guide. Do not use a generic bolt torque chart for wheel fasteners. Always refer to the specific torque in the operator's manual or workshop manual, and re-torque after the first 2 hours of use after any wheel removal.

Metric bolts have the property class stamped on the head — for example "8.8", "10.9" or "12.9". Grade 8.8 bolts are typically plain or silver in colour. Grade 10.9 are often yellow zinc-plated. Grade 12.9 are commonly black (black oxide finish). Bolts without markings should be assumed to be low-grade (4.6 or 4.8) and should not be used as replacements in high-load applications on machinery.

Standard bolts (not torque-to-yield) can generally be reused if they are in good condition — no corrosion, no thread damage, not stretched. Torque-to-yield (TTY) bolts — which are common on engine internals such as cylinder heads and connecting rods — must never be reused. They are designed to stretch past their yield point during tightening, which provides a precise and consistent clamp load. Attempting to retorque or reuse a TTY bolt is dangerous. TTY bolts are usually identified in the service manual as "one-time use" or by an angular tightening specification (e.g. "tighten to 20 Nm + 90°").