Fastener Torque

This page provides the sections on proper bolt torque from Barrett, "Fastener Design Manual," NASA Reference Publication , .

For more information, please visit our website.

Other related chapters from the NASA "Fastener Design Manual" can be seen to the right.

NASA "Fastener Design Manual"

1. Fastener Design Criteria
2. Fastener Torque
3. Loads on Fastener Groups
4. Fatigue Resistant Bolts
5. Rivets and Lockbolts

Fastener Torque

Determining the proper torque for a fastener is the biggest problem in fastener installation. Some of the many variables causing problems are

1. The coefficient of friction between mating threads
2. The coefficient of friction between the bolthead (or nut) and its mating surface
3. The effect of bolt coatings and lubricants on the friction coefficients
4. The percentage of bolt tensile strength to be used for preload
5. Once agreement is reached on item 4, how to accurately determine this value
6. Relative spring rates of the structure and the bolts
7. Interaction formulas to be used for combining simultaneous shear and tension loads on a bolt (Should friction loads due to bolt clamping action be included in the interaction calculations?)
8. Whether "running torque" for a locking device should be added to the normal torque

Development of Torque Tables

The coefficient of friction can vary from 0.04 to 1.10, depending on the materials and the lubricants being used between mating materials. (Table IV from ref. 2 gives a variety of friction coefficients.) Since calculated torque values are a function of the friction coefficients between mating threads and between the bolthead or nut and its mating surface, it is vitally important that the torque table values used are adjusted to reflect any differences in friction coefficients between those used to calculate the table and the user's values. Running torque should be included in the values listed in the tables because any torque puts shear load on the bolt.

The torque values in table V have been calculated as noted in the footnotes, by using formulas from reference 3. (A similar table was published in Product Engineering by Arthur Korn around .)

Higher torques (up to theoretical yield) are sometimes used for bolts that cannot be locked to resist vibration. The higher load will increase the vibration resistance of the bolt, but the bolt will yield and unload if its yield point is inadvertently exceeded. Since the exact yield torque cannot be determined without extensive instrumentation, it is not advisable to torque close to the bolt yield point.

Fastener proof load is sometimes listed in the literature. This value is usually 75 percent of theoretical yield, to prevent inadvertent yielding of the fastener through torque measurement inaccuracies.

Table V -- Bolt Torque

[No lubrication on threads. Torque values are based on friction coefficients of 0.12 between threads and 0.14 between nut and washer or head and washer, as manufactured (no special cleaning).]

Size Root area,
in.2 Torque range
(class 8, 150 ksi, bolts (Note 1)) 10-24 0. 23 to 34 in.-lb 10-32 0. 29 to 43 in.-lb 1/4-20 0. 54 to 81 in.-lb 1/4-28 0. 68 to 102 in.-lb 5/16-18 0. 117 to 176 in.-lb 5/16-24 0. 139 to 208 in.-lb 3/8-16 0. 205 to 308 in.-lb 3/8-24 0. 230 to 345 in. -lb 7/16-14 0. 28 to 42 ft -lb 7/16-20 0. 33 to 50 ft-lb 1/2-13 0. 42 to 64 ft-lb 1/2-20 0. 52 to 77 ft-lb 9/16-12 0. 61 to 91 ft-lb 9/16-18 0. 73 to 109 ft-lb 5/8-11 0. 84 to 126 ft-lb 5/8-18 0. 104 to 156 ft-lb 3/4-10 0. 117 to 176 ft-lb (Note 2) 3/4-16 0. 139 to 208 ft-lb (Note 2) 7/8-9 0. 184 to 276 ft-lb (Note 2) 7/8-14 0. 213 to 320 ft-lb (Note 2) 1-8 0. 276 to 414 ft-lb (Note 2) 1-14 0. 323 to 485 ft-lb (Note 2) 1 1/8-7 0. 390 to 585 ft-lb (Note 2) 1 1/8-12 0. 465 to 698 ft-lb (Note 2) 1 1/4-7 0. 559 to 838 ft-lb (Note 2) 1 1/4-12 1. 655 to 982 ft-lb (Note 2) Note 1:  The values given are 50 and 75 percent of theoretical yield strength of a bolt material with a yield of 120 ksi. Corresponding values for materials with different yield strengths can be obtained by multiplying these table values by the ratio of the respective material yield strengths. Note 2:  Bolts of 0.75-in. diameter and larger have reduced allowables (75 percent of normal strength) owing to inability to heat treat this large a cross section to an even hardness.

Need a Bolted Joint Calculator?

Try this bolted joint calculator.

• stress analysis of a bolted joint
• accounts for preload, applied axial load, and applied shear load

Alternative Torque Formula

A popular formula for quick bolt torque calculations is T = KFd, where T denotes torque, F denotes axial load, d denotes bolt diameter, and K (torque coefficient) is a calculated value from the formula:

$$ K = \left({ d_m \over 2d }\right) { \tan{\psi} + \mu \sec{\alpha} \over 1 - \mu \tan{\psi} \sec{\alpha} } + 0.625 \mu_c $$

$$ K = \left({ d_m \over 2d }\right) { \tan{\psi} + \mu \sec{\alpha} \over 1 - \mu \tan{\psi} \sec{\alpha} } + 0.625 \mu_c $$

as given in reference 4 (p. 378) where

dm

thread mean diameter

ψ

thread helix angle

μ

friction coefficient between threads

α

thread angle

μc

friction coefficient between bolthead (or nut) and clamping surface

The commonly assumed value for K is 0.2, but this value should not be used blindly. Table VI gives some calculated values of K for various friction coefficients. A more realistic "typical" value for K would be 0.15 for steel on steel. Note that μ and μc are not necessarily equal, although equal values were used for the calculated values in table VI.

Table VI -- Torque Coefficients Friction coefficient Torque
Coefficient,

K

Between
threads,

μ

Between bolthead
(or nut) and
clamping surface,

μc

0.05 0.05 0.074 0.10 0.10 0.133 0.15 0.15 0.189 0.20 0.20 0.250

Torque-Measuring Methods

A number of torque-measuring methods exist, starting with the mechanic's "feel" and ending with installing strain gages on the bolt. The accuracy in determining the applied torque values is cost dependent. Tables VII and VIII are by two different "experts," and their numbers vary. However, they both show the same trends of cost versus torque accuracy.

Table VII -- Industrial Fasteners Institute's Torque-Measuring Method

[From ref. 1.]

Preload measuring method Accuracy, percent Relative cost Feel (operator's judgment) ±35 1 Torque wrench ±25 1.5 Turn of the nut ±15 3 Load-indicating washers ±10 7 Fastener elongation ±3 to 5 15 Strain gages ±1 20
Table VIII -- Machine Design's Torque-Measuring Method

[From ref. 5.]

(a) Typical tool accuracies

Type of tool Element controlled Typical accuracy range,
percent of full scale Slug wrench Turn 1 Flat Bar torque wrench Torque ±3 to 15 Turn 1/4 Flat Impact wrench Torque ±10 to 30 Turn ±10 to 20° Hydraulic wrench Torque ±3 to ±10 Turn ±5 to 10° Gearhead air-powered wrench Torque ±10 to ±20 Turn ±5 to 10° Mechanical multiplier Torque ±5 to 20 Turn ±2 to 10° Worm-gear torque wrench Torque ±0.25 to 5 Turn ±1 to 5° Digital torque wrench Torque ±1/4 to 1 Turn 1/4 Flat Ultrasonically controlled wrench Bolt elongation ±1 to 10 Hydraulic tensioner Initial bolt stretch ±1 to 5 Computer-controlled tensioning Simultaneous torque and turn ±0.5 to 2

(b) Control accuracies

Element controlled Preload accuracy, percent To maximize accuracy Torque ±15 to ±30 Control bolt, nut, and washer hardness, dimensions, and finish. Have consistent lubricant conditions, quantities, application, and types. Turn ±15 to ±30 Use consistent snug torque. Control part geometry and finish. Use new sockets and fresh lubes. Torque and turn ±10 to ±25 Plot torque vs turn and compare to previously derived set of curves. Control bolt hardness, finish, and geometry. Torque past yield ±3 to ±l0 Use "soft" bolts and tighten well past yield point. Use consistent snugging torque. Control bolt hardness and dimensons. Bolt stretch ±1 to ±8 Use bolts with flat, parallel ends. Leave transducer engaged during tightening operation. Mount transducer on bolt centerline.

References

Friction bolt(Split sets)

Friction bolt (Split sets)is rollformed into a C shape bolt with slot by high tensile steel band,which one end is tapered

for easily insertingbolt into drillinghole.The other end is welded a ring to hold the bearing plate.

Functions

Friction bolt (Split sets) is a frictional ground support system.When friction bolt is inserted into drilling hole with smaller diameter, the slot partially closes and bolt diameter is compressed, which creates radical forces  on rock roof surface along the whole length and firmly holds the rock.

Features&Advantages

• Made from high strength steel band  

• Immediate frictional Support in axial and radial

• Independent supporting without plate

• Easy for installation

• Simple design,cost saving

• Available in black,cold galvanizing or hot dip galvanized

Mechanical Properties

Technical Data

TRFB33

TRFB39

TRFB42

TRFB47

Drill hole diameter (mm)

30-32

35-38

38-40

43-45.5

Min. Yield strength (kN)

80

90

Goto TRM to know more.

100

120

135

Min. Tensile strength (kN)

100

120

132

165

180

Typ. Tensile strength (kN)

120

135

150

180

200

Elongation (A%)

&#;20

&#;20

&#;20

&#;20

Typ. Anchorage (ton/m)

4-6

4-7

5-8

6-10

Bearing plate (mm)

150x150x4

150x150x4

150x150x4.5

150x150x5

Accessories

Bearing plate,Driver,Pull collar.

Length & Package

• Length:450-mm as specified

• Package:100pcs &#; 300pcs each bundle as specified

Applications

• Mines

• Tunnels

• Slopes

• Places where need ground support

How to work

• The nature of ground must be evaluated.

• Choose the proper bit and drill a hole according to bolt diameter,bolt length,and drilling procedure,and length is at least 150mm longer than length of friction bolt.

• Place a plate onto friction bolt (dome against the ring,tapered end at front).

• Friction bolts must be installed as perpendicular to the rock surface.

• Put driver dolly into bolt and drive friction bolt into the hole until the plate is firmly against the rock surface.

• Do not pound on the friction bolt when plate tightly fixes on the rock surface,in order to avoid damage of  

  friction bolt end.

• Pull tests shall be performed to determine initial anchorage of the friction bolts after installation.

  Additional reading:
  Ultimate Guide to Heavy-Duty Mesh Bolts

What is Chemical Cleaning in Piping?
Electric Heat Tracing Design: Ensuring Optimal Efficiency and Performance
Electrical Tracing on Pipe

Fastener Torque

Friction BoltFriction Bolt/Split Set bolts