Class 12.9 bolt torque chart and strength

An M12 x 1.75 class 12.9 bolt takes 109 ft-lb (147 N·m) plain and dry or 81 ft-lb (110 N·m) oiled, for 61.3 kN of clamp load. That is about 17% more than 10.9. Proof stress is 970 MPa in every size.

By the Torque Reference editors 5 sources cited Last reviewed 21 Oct 2026 Method

Contents8 sections

Key takeaways

12.9 means 1,200 MPa nominal tensile strength with yield at 0.9 of that ⁠¹.
Proof 970 MPa, yield 1,100 MPa, tensile 1,220 MPa, in every size ⁠¹.
No SAE J429 grade reaches 12.9: Grade 8 is 120 ksi proof, while 12.9 is 141 ksi.
Check the nut. A legacy class 12 nut is listed just below the 12.9 tensile strength ⁠².

Quick facts

Proof stress	970 MPa (140.7 ksi)
Tensile	1,220 MPa (176.9 ksi)
Head marking	12.9 plus maker's mark
vs 10.9 torque	+17%

Class 12.9 strength

Sizes	Proof stress	Yield	Tensile
All sizes	970 MPa	1100 MPa	1220 MPa

Sizes

Proof stress

Yield

Tensile

All sizes

970 MPa

1100 MPa

1220 MPa

ISO 898-1 Table 3⁠¹.

Class 12.9 torque chart

Size	Dry K 0.20⁠²	Zinc K 0.18⁠²	Oiled K 0.15⁠²
M3 x 0.5	19 in-lb2.2 N·m	17 in-lb2.0 N·m	15 in-lb1.6 N·m
M4 x 0.7	45 in-lb5.1 N·m	41 in-lb4.6 N·m	34 in-lb3.8 N·m
M5 x 0.8	91 in-lb10 N·m	82 in-lb9.3 N·m	69 in-lb7.7 N·m
M6 x 1	13 ft-lb18 N·m	12 ft-lb16 N·m	116 in-lb13 N·m
M8 x 1.25	31 ft-lb43 N·m	28 ft-lb38 N·m	24 ft-lb32 N·m
M10 x 1.5	62 ft-lb84 N·m	56 ft-lb76 N·m	47 ft-lb63 N·m
M12 x 1.75	109 ft-lb147 N·m	98 ft-lb132 N·m	81 ft-lb110 N·m
M14 x 2	173 ft-lb234 N·m	155 ft-lb211 N·m	130 ft-lb176 N·m
M16 x 2	270 ft-lb365 N·m	243 ft-lb329 N·m	202 ft-lb274 N·m
M20 x 2.5	526 ft-lb713 N·m	473 ft-lb642 N·m	394 ft-lb535 N·m
M24 x 3	909 ft-lb1,233 N·m	818 ft-lb1,109 N·m	682 ft-lb925 N·m
M30 x 3.5	1,806 ft-lb2,449 N·m	1,626 ft-lb2,204 N·m	1,355 ft-lb1,837 N·m

Size

Dry K 0.20⁠²

Zinc K 0.18⁠²

Oiled K 0.15⁠²

M3 x 0.5

19 in-lb2.2 N·m

17 in-lb2.0 N·m

15 in-lb1.6 N·m

M4 x 0.7

45 in-lb5.1 N·m

41 in-lb4.6 N·m

34 in-lb3.8 N·m

M5 x 0.8

91 in-lb10 N·m

82 in-lb9.3 N·m

69 in-lb7.7 N·m

M6 x 1

13 ft-lb18 N·m

12 ft-lb16 N·m

116 in-lb13 N·m

M8 x 1.25

31 ft-lb43 N·m

28 ft-lb38 N·m

24 ft-lb32 N·m

M10 x 1.5

62 ft-lb84 N·m

56 ft-lb76 N·m

47 ft-lb63 N·m

M12 x 1.75

109 ft-lb147 N·m

98 ft-lb132 N·m

81 ft-lb110 N·m

M14 x 2

173 ft-lb234 N·m

155 ft-lb211 N·m

130 ft-lb176 N·m

M16 x 2

270 ft-lb365 N·m

243 ft-lb329 N·m

202 ft-lb274 N·m

M20 x 2.5

526 ft-lb713 N·m

473 ft-lb642 N·m

394 ft-lb535 N·m

M24 x 3

909 ft-lb1,233 N·m

818 ft-lb1,109 N·m

682 ft-lb925 N·m

M30 x 3.5

1,806 ft-lb2,449 N·m

1,626 ft-lb2,204 N·m

1,355 ft-lb1,837 N·m

Calculated with T = K × D × F, where F is 75% of the bolt’s proof load⁠² and K is the nut factor for each condition. Real preload from a torque wrench scatters by about ±25%⁠³. When the equipment maker gives a torque, use theirs. How these numbers are made.

What 12.9 means

“12” is the nominal tensile strength in hundreds of MPa, and “.9” means yield is 90% of it ⁠¹. Class 12.9 is the strongest class on this site. Its minimums are 970 MPa proof stress, 1,100 MPa 0.2% proof strength (yield) and 1,220 MPa tensile, in every size ⁠¹. ISO 898-1 covers carbon and alloy steel bolts ⁠¹. The material and heat-treatment clause is not in the free preview this site used, so it is not summarized here.

The head carries “12.9” and the maker’s identification mark. A leading zero marks reduced loadability ⁠¹.

Torque and clamp load

ISO tabulates the M12 12.9 proof load as 81,800 N ⁠¹. The chart uses 75% of it, 61.3 kN, as the clamp load ⁠². That gives 109 ft-lb dry, 98 ft-lb zinc-plated and 81 ft-lb oiled. At M8 the values are 31, 28 and 24 ft-lb. At M6 the dry value is 13 ft-lb (18 N·m).

At the same size and condition:

10.9: 12.9 takes 970 ÷ 830, about 17% more, in every size.
8.8: 12.9 takes about 67% more up to M16, and 62% more above.
4.6: 12.9 takes 4.3 times as much.

The gap between 12.9 and 10.9 is small. Getting the condition right (dry, plated or oiled) matters more than the class, because the dry and oiled columns differ by 33%.

No SAE equivalent

Converted, 970 MPa proof is 140.7 ksi and 1,220 MPa tensile is 176.9 ksi ⁠⁴. SAE J429 Grade 8 stops at 120 ksi proof and 150 ksi tensile ⁠². Structural ASTM F3125 Grade A490 has a 150 ksi minimum and a 173 ksi maximum tensile strength ⁠⁵, so 12.9’s minimum sits above A490’s maximum. None of these is a substitute for a specified 12.9 bolt.

Matching nut

The nut’s proof strength should be at least the bolt’s tensile strength ⁠². The older ISO 898-2 table, as reproduced by Fastenal, lists class 12 nuts at 1,140–1,200 MPa depending on size ⁠². That is just under 12.9’s 1,220 MPa tensile, so on those figures the rule is not strictly met. The current ISO 898-2 values were not verified for this page. Use the nut the bolt or equipment maker specifies.

A 12.9 bolt in a tapped hole in softer material needs the same check. The internal thread can strip before the bolt reaches its clamp load. In that case, the joint, not the bolt class, sets the torque.

Sources

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