Grade 8 bolt torque chart and strength

A 1/2-13 Grade 8 bolt takes 107 ft-lb plain and dry or 80 ft-lb oiled, for 12,780 lbf of clamp load. That is about 41% more than Grade 5 in every size. Grade 8 holds 120 ksi proof strength from 1/4 to 1-1/2 in.

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

Contents9 sections

Key takeaways

Grade 8 is medium carbon alloy steel, quenched and tempered ⁠¹.
Six radial lines, 60° apart, mark the head ⁠¹.
There is no strength break: 120 ksi proof, 130 ksi yield and 150 ksi tensile from 1/4 to 1-1/2 in ⁠¹.
Pair it with a Grade 8 nut. A Grade 5 nut is not strong enough ⁠¹.

Quick facts

Material	Medium carbon alloy steel, quenched and tempered ⁠¹
Head marking	6 radial lines
Proof, all sizes	120,000 psi
Metric near-equivalent	Class 10.9

Grade 8 strength

Sizes	Proof stress	Yield	Tensile
1/4 to 1-1/2 in	120,000 psi	130,000 psi	150,000 psi

Sizes

Proof stress

Yield

Tensile

1/4 to 1-1/2 in

120,000 psi

130,000 psi

150,000 psi

SAE J429 values as tabulated by Fastenal⁠¹.

Grade 8 torque chart

Size	Dry K 0.20⁠¹	Zinc K 0.18⁠¹	Oiled K 0.15⁠¹
1/4-20	12 ft-lb16 N·m	11 ft-lb15 N·m	107 in-lb12 N·m
5/16-18	25 ft-lb33 N·m	22 ft-lb30 N·m	18 ft-lb25 N·m
3/8-16	44 ft-lb59 N·m	39 ft-lb53 N·m	33 ft-lb44 N·m
7/16-14	70 ft-lb94 N·m	63 ft-lb85 N·m	52 ft-lb71 N·m
1/2-13	107 ft-lb144 N·m	96 ft-lb130 N·m	80 ft-lb108 N·m
9/16-12	154 ft-lb208 N·m	138 ft-lb187 N·m	115 ft-lb156 N·m
5/8-11	212 ft-lb287 N·m	191 ft-lb259 N·m	159 ft-lb215 N·m
3/4-10	377 ft-lb511 N·m	339 ft-lb460 N·m	283 ft-lb383 N·m
7/8-9	606 ft-lb822 N·m	546 ft-lb740 N·m	455 ft-lb617 N·m
1-8	909 ft-lb1,232 N·m	818 ft-lb1,109 N·m	682 ft-lb924 N·m

Size

Dry K 0.20⁠¹

Zinc K 0.18⁠¹

Oiled K 0.15⁠¹

1/4-20

12 ft-lb16 N·m

11 ft-lb15 N·m

107 in-lb12 N·m

5/16-18

25 ft-lb33 N·m

22 ft-lb30 N·m

18 ft-lb25 N·m

3/8-16

44 ft-lb59 N·m

39 ft-lb53 N·m

33 ft-lb44 N·m

7/16-14

70 ft-lb94 N·m

63 ft-lb85 N·m

52 ft-lb71 N·m

1/2-13

107 ft-lb144 N·m

96 ft-lb130 N·m

80 ft-lb108 N·m

9/16-12

154 ft-lb208 N·m

138 ft-lb187 N·m

115 ft-lb156 N·m

5/8-11

212 ft-lb287 N·m

191 ft-lb259 N·m

159 ft-lb215 N·m

3/4-10

377 ft-lb511 N·m

339 ft-lb460 N·m

283 ft-lb383 N·m

7/8-9

606 ft-lb822 N·m

546 ft-lb740 N·m

455 ft-lb617 N·m

1-8

909 ft-lb1,232 N·m

818 ft-lb1,109 N·m

682 ft-lb924 N·m

Calculated with T = K × D × F, where F is 75% of the bolt’s proof load⁠¹ and K is the nut factor for each condition. Real preload from a torque wrench scatters by about ±25%⁠². When the equipment maker gives a torque, use theirs. How these numbers are made.

Material and marking

SAE J429 Grade 8 is medium carbon alloy steel, quenched and tempered to a core hardness of Rockwell C33–C39 ⁠¹. The head carries six radial lines 60° apart ⁠¹.

Grade 8.2 has the same proof, yield and tensile strength as Grade 8 from 1/4 to 1 in. It is made from low-carbon boron steel, also quenched and tempered, and uses a different radial “sunburst” head pattern ⁠¹. This chart’s Grade 8 values apply to it in those sizes.

Strength

Grades 2 and 5 step down in larger sizes. Grade 8 does not: it holds 120 ksi proof, 130 ksi yield and 150 ksi tensile across the whole J429 range of 1/4 to 1-1/2 in ⁠¹. Torque therefore rises smoothly with size. The 1-8 bolt takes 909 ft-lb dry for a 54,540 lbf clamp load.

Compared with other grades

At the same size and condition:

Grade 5: Grade 8 takes 120 ÷ 85, or about 41% more torque, in every size up to 1 in. At 3/8-16 that is 44 against 31 ft-lb dry.
Grade 2: 2.2 times the Grade 2 torque up to 3/4 in, and 3.6 times at 7/8 and 1 in, where Grade 2 drops to 33 ksi proof.
Metric class 10.9: almost the same strength. Grade 8’s 120 ksi proof is 827 MPa, against 830 MPa for 10.9 ⁠³.
Structural A490 (F3125): 150 ksi minimum tensile like Grade 8, with a 173 ksi maximum ⁠⁴. A490 bolts follow RCSC installation rules, not torque tables ⁠⁵.

Matching nut

Use an SAE J995 Grade 8 nut ⁠¹. Its 150 ksi proof stress equals the bolt’s tensile strength. A Grade 5 nut, at 120 ksi on UNC threads ⁠¹, falls short of the rule that the nut’s proof strength should be at least the bolt’s tensile strength. The nut threads can then strip before the bolt reaches its clamp load. The same applies to a Grade 8 bolt in a tapped hole in softer material.

Dry vs lubricated

For the same 12,780 lbf clamp on a 1/2-13 bolt, the chart gives 107 ft-lb dry (K 0.20), 96 ft-lb zinc-plated (K 0.18) and 80 ft-lb oiled (K 0.15) ⁠¹. The oiled value is the one many charts print without a label. Applied to a dry bolt, it leaves about 25% less clamp load than intended. The dry value applied to an oiled bolt overshoots by a third. The dry vs lubricated guide explains the difference.

Sources

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