Rotational Force applied to bolts and nuts

Torque is a measure of the rotational force applied to an object, often expressed in units like Newton-meters (N m) or foot-pounds (ft-lb).

In the context of bolts, screws, and nuts, torque is crucial for ensuring proper assembly and maintaining the integrity of the joint.

However, not every screw has the same strength class or thread size, which is why the required torque also varies.

Screw and Bolt Torque Table for Standard Threads

The recommended tightening torques below are a great starting point for figuring out how much torque you need.

Please note:

Keep in mind that you might need to adjust these numbers depending on the specific connection or how much lubrication is used on the fasteners.

This Chart gives the suggested maximum torque values for threaded products, but it's just a reference.

Thread Size	Torque for Standard Threads in [Nm]
Bolt Grade	3.6	4.6	5.6	6.8	8.8	10.9	12.9
M2	0,1	0,13	0,16	0,26	0,35	0,49	0,59
M2,5	0,2	0,27	0,34	0,54	0,72	1,01	1,21
M3	0,35	0,48	0,60	0,96	1,28	1,80	2,16
M4	0,81	1,12	1,39	2,23	2,97	4,18	5,02
M5	0,6	2,26	2,83	4,52	6,03	8,48	10,18
M6	2,8	3,84	4,80	7,69	10,25	14,41	17,29
M7		5,13	6,42	10,27	13,70	19,25	23,10
M8		9,35	11,69	18,70	24,93	35,06	42,07
M10		18	23	37	49	70	83
M12		32	40	65	86	121	146
M14		52	65	104	138	194	233
M16		81	101	161	215	302	363
M18		112	139	222	296	417	500
M20		157	197	315	420	590	709
M22		215	269	430	574	807	968
M24		272	340	544	726	1020	1224
M27		400	500	800	1067	1500	1800
M30		542	677	1083	1445	2032	2438
M33		739	923	1477	1969	2770	3323
M36		948	1185	1896	2528	3555	4266
M39		1229	1536	2457	3276	4607	5529
M42		1519	1899	3038	4050	5696	6835
M45		1898	2373	3796	5062	7118	8541
M48		2282	2853	4565	6086	8559	10271
M52		2954	3692	5907	7876	11076	13292
M56		3672	4591	7345	9793	13772	16526
M60		4582	5728	9164	12219	17183	20619
M64		5536	6920	11071	14762	20759	24911
M68		6720	8400	13440	17919	25199	30239

What is torque?

Torque is a physical force that indicates how strongly a rotational movement affects an object.

Torque is a measure of the rotational force applied to an object, causing it to rotate around an axis or pivot point. It's calculated as the product of force and the distance from the pivot (known as the lever arm). In simpler terms, torque measures how much a force can make something twist or spin, like turning a wrench to loosen a bolt. It's usually measured in units like Newton-meters (Nm) or foot-pounds (ft-lb).

How can you calculate torque for bolts?

For those without a reference book at hand, it is always possible to calculate the tightening torque yourself.

The torque, or tightening moment, is expressed in Newton meters [Nm].

To calculate torque for bolts, you can use the following formula:

To calculate the torque (M) in Newton meters [N m], you will need the force (F) in Newtons [N] and the lever arm distance (l) measured perpendicular to the line of action in meters [m].

The direction of the torque is indicated by + (counterclockwise) and — (clockwise).

What strength classes are there?

The strength classes of screws determine their tensile strength R_m and yield strength R_e.

The class is represented on the screw head by two numbers separated by a dot.

In the illustration below, the left number signifies the tensile strength, and the right number represents the yield strength.

Thanks to the various number combinations, different types of bolts can be compared with each other.

How to calculate tensile strength?

To calculate tensile strength, simply multiply the left number of the strength class by 100.

How to calculate yield strength?

To calculate yield strength, multiply the left and right numbers, and then multiply the result by 10.

Table of strength classes of bolts

The following table includes all the strength classes mentioned in the screw torque table, along with their corresponding tensile strength and yield strength.

Strength Class	Tensile Strength	Yield Strength
3.6	3 x 100 = 300 N/mm²	3 x 6 x 10 = 180 N/mm²
4.6	4 x 100 = 400 N/mm²	4 x 6 x 10 = 240 N/mm²
4.8	4 x 100 = 400 N/mm²	4 x 8 x 10 = 320 N/mm²
5.6	5 x 100 = 500 N/mm²	5 x 6 x 10 = 300 N/mm²
5.8	5 x 100 = 500 N/mm²	5 x 8 x 10 = 400 N/mm²
6.8	6 x 100 = 600 N/mm²	6 x 8 x 10 = 480 N/mm²
8.8	8 x 100 = 800 N/mm²	8 x 8 x 10 = 640 N/mm²
9.8	9 x 100 = 900 N/mm²	9 x 8 x 10 = 720 N/mm²
10.9	10 x 100 = 1000 N/mm²	10 x 9 x 10 = 900 N/mm²
12.9	12 x 100 = 1200 N/mm²	12 x 9 x 10 = 1080 N/mm²

Which strength class suits which screw?

Screws made of aluminum, stainless steel, and titanium possess different properties due to their distinct materials.

The following table is intended to assist in assigning them to their respective strength classes.

Type of Screws	Strength Class
Aluminum Screws	5.6
V2A Screws (stainless steel)	6.8
Titanium Screws	8.8

FAQ

When does a screw break?

When the permissible yield strength is exceeded, the screw begins to deform, eventually leading to the breaking of the screw.

What is the torque for car steel rims?

The correct torque for the wheel bolts of a steel rim on a vehicle can be found in the vehicle manual. However, it usually ranges between 80 and 160 Newton meters.

How much Nm can be applied by hand?

Using a screwdriver, a torque of 30 Nm can be achieved. The longer the lever, the greater the force that can be applied.

Which screws should be tightened with how much Nm?

To find out which screws should be tightened with how much torque, it's worth taking a look at the screw torque table depicted above. There, screws with their respective strength classes and corresponding torques can be easily read.

Where do I find the tightening torque?

Normally, each manufacturer specifies the permissible tightening torque of the screws on the packaging. If that's not the case, it can be found in a screw torque table.

Why do I need a torque testing device for a nutrunner?

Torque testing devices verify the accuracy of torque wrenches, electric nutrunners, and cordless nutrunners so that they can be calibrated accordingly.