Class 4.6 bolt torque chart and strength

An M10 class 4.6 bolt takes 14 ft-lb (20 N·m) plain and dry or 11 ft-lb (15 N·m) oiled, about 39% of the class 8.8 value. Class 4.6 has a proof stress of 225 MPa in every size.

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

Contents9 sections

Key takeaways

4.6 means 400 MPa nominal tensile strength with yield at 0.6 of that ⁠¹.
Proof 225 MPa, yield 240 MPa, tensile 400 MPa, with no size break ⁠¹.
Class 8.8 takes 2.6 times the 4.6 torque up to M16 and 2.7 times above.
By strength it matches SAE Grade 2 in sizes above 3/4 in.

Quick facts

Proof stress	225 MPa (32.6 ksi)
Tensile	400 MPa (58 ksi)
Head marking	4.6 plus maker's mark
Inch near-equivalent	Grade 2, 7/8 in and up

Class 4.6 strength

Sizes	Proof stress	Yield	Tensile
All sizes	225 MPa	240 MPa	400 MPa

Sizes

Proof stress

Yield

Tensile

All sizes

225 MPa

240 MPa

400 MPa

ISO 898-1 Table 3⁠¹.

Class 4.6 torque chart

Size	Dry K 0.20⁠²	Zinc K 0.18⁠²	Oiled K 0.15⁠²
M3 x 0.5	5 in-lb0.5 N·m	4 in-lb0.5 N·m	3 in-lb0.4 N·m
M4 x 0.7	10 in-lb1.2 N·m	9 in-lb1.1 N·m	8 in-lb0.9 N·m
M5 x 0.8	21 in-lb2.4 N·m	19 in-lb2.2 N·m	16 in-lb1.8 N·m
M6 x 1	36 in-lb4.1 N·m	32 in-lb3.7 N·m	27 in-lb3.1 N·m
M8 x 1.25	87 in-lb9.9 N·m	79 in-lb8.9 N·m	66 in-lb7.4 N·m
M10 x 1.5	14 ft-lb20 N·m	13 ft-lb18 N·m	11 ft-lb15 N·m
M12 x 1.75	25 ft-lb34 N·m	23 ft-lb31 N·m	19 ft-lb26 N·m
M14 x 2	40 ft-lb54 N·m	36 ft-lb49 N·m	30 ft-lb41 N·m
M16 x 2	63 ft-lb85 N·m	56 ft-lb76 N·m	47 ft-lb64 N·m
M20 x 2.5	122 ft-lb165 N·m	110 ft-lb149 N·m	91 ft-lb124 N·m
M24 x 3	211 ft-lb286 N·m	190 ft-lb257 N·m	158 ft-lb214 N·m
M30 x 3.5	419 ft-lb568 N·m	377 ft-lb511 N·m	314 ft-lb426 N·m

Size

Dry K 0.20⁠²

Zinc K 0.18⁠²

Oiled K 0.15⁠²

M3 x 0.5

5 in-lb0.5 N·m

4 in-lb0.5 N·m

3 in-lb0.4 N·m

M4 x 0.7

10 in-lb1.2 N·m

9 in-lb1.1 N·m

8 in-lb0.9 N·m

M5 x 0.8

21 in-lb2.4 N·m

19 in-lb2.2 N·m

16 in-lb1.8 N·m

M6 x 1

36 in-lb4.1 N·m

32 in-lb3.7 N·m

27 in-lb3.1 N·m

M8 x 1.25

87 in-lb9.9 N·m

79 in-lb8.9 N·m

66 in-lb7.4 N·m

M10 x 1.5

14 ft-lb20 N·m

13 ft-lb18 N·m

11 ft-lb15 N·m

M12 x 1.75

25 ft-lb34 N·m

23 ft-lb31 N·m

19 ft-lb26 N·m

M14 x 2

40 ft-lb54 N·m

36 ft-lb49 N·m

30 ft-lb41 N·m

M16 x 2

63 ft-lb85 N·m

56 ft-lb76 N·m

47 ft-lb64 N·m

M20 x 2.5

122 ft-lb165 N·m

110 ft-lb149 N·m

91 ft-lb124 N·m

M24 x 3

211 ft-lb286 N·m

190 ft-lb257 N·m

158 ft-lb214 N·m

M30 x 3.5

419 ft-lb568 N·m

377 ft-lb511 N·m

314 ft-lb426 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 the class number means

In ISO 898-1, the first number is the nominal tensile strength divided by 100 MPa. The second is ten times the ratio of yield to tensile strength ⁠¹. Class 4.6 is therefore 400 MPa nominal tensile, with yield at 60% of it. The standard’s minimums are 225 MPa proof stress, 240 MPa lower yield strength and 400 MPa tensile, the same in every size ⁠¹. ISO 898-1 covers bolts of carbon steel and alloy steel ⁠¹. The free preview this site checked does not include the material and heat-treatment table, so this page does not describe them.

Marking

The head carries “4.6” and the manufacturer’s identification mark ⁠¹. A leading zero (“04.6”) marks a bolt with reduced loadability ⁠¹. Full-class torque values do not apply to those bolts.

Torque compared with other classes

At the same size and condition, torque scales with proof stress:

Torque of other classes as a multiple of class 4.6, same size and condition
Class	Up to M16	Above M16
8.8	2.58 ×	2.67 ×
10.9	3.69 ×	3.69 ×
12.9	4.31 ×	4.31 ×

So 4.6 values are small. An M8 class 4.6 bolt is 87 in-lb (9.9 N·m) dry. That is below 10 ft-lb, which is why the chart shows it in in-lb. An M12 is 25 ft-lb (34 N·m). Setting an 8.8 value on a 4.6 bolt would ask for a clamp load well past the bolt’s proof load. At M12, the 8.8 dry torque targets 36.7 kN against a class 4.6 proof load of about 19 kN.

Inch equivalents

Converted to inch units, 225 MPa proof is 32.6 ksi and 400 MPa tensile is 58 ksi ⁠⁴. SAE Grade 2 above 3/4 in is rated at 33 ksi proof and 60 ksi tensile ⁠², so the two are nearly equal. Grade 2 from 1/4 to 3/4 in, at 55 ksi proof, is stronger. ASTM A307 Grade A bolts have a similar 60 ksi minimum tensile strength, but A307 specifies no proof load ⁠⁵, so a torque for them needs a different basis.

Matching nut

The rule is a nut whose proof strength is at least the bolt’s tensile strength ⁠². The older ISO 898-2 table lists class 8 nuts at 800 MPa or more proof in every size ⁠². That is twice the 400 MPa tensile strength of a 4.6 bolt, so any class 8 nut is enough.

Sources

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