Question 1

What torque should I use for an M12 bolt?

Accepted Answer

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. If the bolt is dry (no lubricant), increase the torque by around 25%. If copper anti-seize is applied, reduce by around 20%. Always check for a manufacturer figure for critical joints.

Question 2

What is the difference between grade 8.8, 10.9 and 12.9 bolts?

Accepted Answer

The numbers refer to the property class (strength) of the bolt. Grade 8.8 is medium-strength carbon steel — the most common general-purpose bolt. Grade 10.9 is high-strength alloy steel, used in machinery and structural joints. Grade 12.9 is the highest common grade, very high 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.

Question 3

Does using copper slip (anti-seize) change the required torque?

Accepted Answer

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

Question 4

How do I read the markings on a bolt head?

Accepted Answer

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 plain or 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 in high-load applications.

Question 5

What torque for tractor wheel nuts?

Accepted Answer

Tractor wheel nut torque must always come from the manufacturer's service manual — it varies significantly by make, model and wheel size. Typical values range from 390 Nm to 680 Nm for agricultural tractors, but this is just a guide. Do not use generic bolt torque charts for wheel fasteners — always refer to the specific torque in the operator's manual or workshop manual.

Question 6

What torque wrench do I need for farm machinery?

Accepted Answer

For general farm 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 wheel bolts, 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.

Size	Pitch (mm)	Grade 8.8 (Nm)	Range (Nm)
M5	0.80	5.5	5–6
M6common	1.00	9.5	9–10
M8common	1.25	23	21–25
M10common	1.50	46	41–51
M12common	1.75	79	71–87
M14	2.00	125	113–138
M16common	2.00	195	176–215
M18	2.50	270	243–297
M20	2.50	385	347–424
M22	2.50	520	468–572
M24	3.00	660	594–726
M27	3.00	980	882–1078
M30	3.50	1320	1188–1452

Bolt Torque Settings Calculator

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Reference Table — Lightly Oiled, Coarse Thread

Lubrication Condition Guide

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