Bolt Torque Chart: SAE Grades and Metric Classes

Tightening a bolt stretches it slightly, like a stiff spring, and that stretch is what clamps the parts together. Too little torque and the joint works loose; too much and the bolt yields or strips its threads. The right torque depends on the bolt’s size, its strength grade and whether the threads are dry or lubricated.

Always use the manufacturer’s torque spec when there is one (car wheels, engines, bike parts, machinery). The charts below are general values for standard steel bolts when no spec is given.

SAE bolt torque chart (coarse thread)

Dry threads (ft-lb):

Bolt	Grade 2	Grade 5	Grade 8
1/4-20	5	8	12
5/16-18	11	17	25
3/8-16	20	31	44
7/16-14	32	49	70
1/2-13	49	75	106
9/16-12	70	109	154
5/8-11	97	150	212
3/4-10	172	267	376
7/8-9	167	429	606
1-8	250	644	909

Oiled threads (ft-lb):

Bolt	Grade 2	Grade 5	Grade 8
1/4-20	4	6	9
5/16-18	8	13	18
3/8-16	15	23	33
7/16-14	24	37	52
1/2-13	37	57	80
9/16-12	53	82	115
5/8-11	73	113	159
3/4-10	129	200	282
7/8-9	125	322	455
1-8	187	483	681

Grade 2 drops at 7/8 inch because larger grade 2 bolts are made from weaker steel. For 1/4 and 5/16 bolts, many people find inch-pounds easier: multiply by 12 (8 ft-lb = 96 in-lb).

Metric bolt torque chart (coarse thread)

Dry threads (N·m):

Bolt	Class 8.8	Class 10.9	Class 12.9
M5	6	9	10
M6	10	15	18
M8	25	37	43
M10	50	72	84
M12	88	126	147
M14	141	201	235
M16	218	312	365
M20	441	610	712
M24	761	1053	1231

Oiled threads (N·m):

Bolt	Class 8.8	Class 10.9	Class 12.9
M5	5	7	8
M6	8	11	13
M8	19	27	32
M10	38	54	63
M12	66	94	110
M14	105	151	176
M16	164	234	274
M20	331	457	534
M24	571	790	923

To get ft-lb, divide by 1.356: an M10 8.8 bolt at 50 N·m is about 37 ft-lb.

How these values are worked out

Both charts use the standard short-form formula:

Torque = K × diameter × clamp load

• The clamp load is 75% of the bolt’s proof load (the most it can stretch and spring back fully), the usual target for reusable joints.
• K is the friction factor: about 0.20 for clean, dry steel and 0.15 for oiled threads.
• Proof strengths are from SAE J429 (grade 2, 5, 8) and ISO 898-1 (classes 8.8, 10.9, 12.9).

Plating, thread locker and anti-seize all change K. Zinc-plated bolts are close to the dry values; anti-seize is lower than oil, often K ≈ 0.12, so use even less torque.

Bolt grade markings

Head marking	Grade or class	Tensile strength	Typical use
No marks	SAE grade 2	60–74 ksi	Light duty, furniture, general hardware
3 radial lines	SAE grade 5	105–120 ksi	Cars, machinery, most structural uses
6 radial lines	SAE grade 8	150 ksi	Suspension, heavy equipment, high stress
8.8	Metric class 8.8	800–830 MPa	Equivalent to grade 5
10.9	Metric class 10.9	1040 MPa	Equivalent to grade 8
12.9	Metric class 12.9	1220 MPa	Socket head cap screws, high stress

The marks are also printed with the maker’s logo. Stainless steel bolts (marked A2 or A4, or 18-8 and 316 in the US) are weaker than grade 5 and gall easily: use about the grade 2 values, with anti-seize.

Tips for tightening

• Tighten in stages. On a flange, wheel or cover, go around in a star pattern at about 50%, then 100% of the torque.
• Use the right range of wrench. Torque wrenches are most accurate in the middle of their scale: a 1/4 inch drive (in-lb) wrench for small bolts, 3/8 inch for most car work, 1/2 inch for lug nuts and suspension.
• Turn smoothly and stop at the click. Jerking the wrench overshoots the setting.
• Don’t reuse stretched bolts. Torque-to-yield bolts, common on engine heads, are single-use; the service manual says so.

Not sure of the bolt size? Measure it with the screw and bolt size chart and find the wrench in the wrench size chart.

More DIY charts: tap drill sizes · washer sizes · thread pitch · number and letter drill sizes.