Estimated reading time: 4 minutes

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 SizeTorque for Standard Threads in [N m]
Bolt Grade3.64.65.66.88.810.912.9
M20,10,130,160,260,350,490,59
M2,50,20,270,340,540,721,011,21
M30,350,480,600,961,281,802,16
M40,811,121,392,232,974,185,02
M50,62,262,834,526,038,4810,18
M62,83,844,807,6910,2514,4117,29
M75,136,4210,2713,7019,2523,10
M89,3511,6918,7024,9335,0642,07
M10182337497083
M1232406586121146
M145265104138194233
M1681101161215302363
M18112139222296417500
M20157197315420590709
M22215269430574807968
M2427234054472610201224
M27400500800106715001800
M305426771083144520322438
M337399231477196927703323
M3694811851896252835554266
M39122915362457327646075529
M42151918993038405056966835
M45189823733796506271188541
M482282285345656086855910271
M5229543692590778761107613292
M5636724591734597931377216526
M60458257289164122191718320619
M645536692011071147622075924911
M686720840013440179192519930239

What is torque?

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

Formula symbol:

The formula symbol for torque is M.

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].

Calcu­la­tion of Newton meters

{Nm=1{\frac {kg * m^{2}} {s^{2}}}}

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].

Formula for calcu­la­ting torque

M=F * l

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 this repre­sen­ta­tion, the left number signi­fies the tensile strength, and the right number repres­ents the yield strength.

Strength Classes of Screws

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.

Calcu­la­ting tensile strength

{R_m}=leftNumber * 100 or {R_m}={\frac N {mm^2}}

How to calcu­late yield strength?

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

Calcu­la­ting yield strength

{R_e = leftN­umber * rightN­umber * 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 ClassTensile StrengthYield Strength
3.63 x 100 = 300 N/mm²3 x 6 x 10 = 180 N/mm²
4.64 x 100 = 400 N/mm²4 x 6 x 10 = 240 N/mm²
4.84 x 100 = 400 N/mm²4 x 8 x 10 = 320 N/mm²
5.65 x 100 = 500 N/mm²5 x 6 x 10 = 300 N/mm²
5.85 x 100 = 500 N/mm²5 x 8 x 10 = 400 N/mm²
6.86 x 100 = 600 N/mm²6 x 8 x 10 = 480 N/mm²
8.88 x 100 = 800 N/mm²8 x 8 x 10 = 640 N/mm²
9.89 x 100 = 900 N/mm²9 x 8 x 10 = 720 N/mm²
10.910 x 100 = 1000 N/mm²10 x 9 x 10 = 900 N/mm²
12.912 x 100 = 1200 N/mm²12 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 ScrewsStrength Class
Aluminum Screws5.6
V2A Screws (stain­less steel)6.8
Titanium Screws8.8

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 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 N m can be applied by hand?

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

Which screws should be tightened with how much N m?

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 screwdrivers?

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

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