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TIGHTENING
TORQUE AND TENSILE LOAD
• Application of the correct force (tensile load) is essential
for a reliable assembly:
– undertightened fasteners can work loose;
– overtightened fasteners may distort components or shear.
• Tensile load depends on tightening torque and friction coefficient.
Tensile load (Fo)
The force in newtons (N) which maintains pressure contact between
assembled components.
Tightening torque (Cs)
The product of a force and the leverage length at which it is applied:
Torque (N·m) = Force (in newtons) x Length (in metres).
HOW TIGHT A TORQUE ?
1. Always observe equipment manufacturer's specifications.
2. If none are available, determine required torque on a test
rig.
3. Otherwise, refer to national standards.
Tightening torque table
Torque values are given for 85% fastener yield strength, for class
"A" torque control accuracy (< ±5%).
1. Friction coefficient
Actual friction coefficient depends on fastener and component
condition, and affects tightening. Choose the appropriate table
according to type of fasteners used (i.e. µ = 0,10, 0,15 or 0,20).
2. Fastener class (grade)
The class (grade) of a fastener denotes its strength quality (best is normally 12.9). Check
the appropriate column for the fasteners used.
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3.
Tightening torque (Cs)
Torque values are listed in newton-metre (N·m) for each type
of fastener.
4. Tensile load (Fo)
This force in newtons (N) is the equivalent of an Fo max value.
The above information, for which Facom/Maryland Metrics accepts
no liability, is given as a guide only.
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Conversion
table
The internationally accepted unit is the newton-metre (N·m)
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1.
To convert N·m:
• Newton metres to kilogramme force metres
1 N·m = 0,102 kgf·m
• Newton metres to pound force feet
1 N·m = 0,738 lbf.ft
• Newton metres to pound force inches
1 N·m = 8,851 lbf.in
• Newton metres to ounce force inches
1 N·m = 141,61 ozf.in
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2.
To convert kgf·m:
• Kilogramme force metres to newton metres
1 kgf·m = 9,81 N·m
• Kilogramme force metres to pound force feet
1 kgf·m = 7,23 lbf.ft
• Kilogramme force metres to pound force inches
1 kgf·m = 86,8 lbf.in
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3.
To convert lbf f:
• Pound force feet to newton metres
1 lbf.ft = 1,35 N·m
• Pound force feet to kilogramme force metres
1 lbf.ft = 0,138 kgf·m
• Pound force feet to pound force inches
1 lbf.ft = 12 lbf.in
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4.
To convert lbf.in:
• Pound force inches to newton metres
1 lbf.in = 0,1129 N·m
• Pound force inches to kilogramme force metres
1 lbf.in = 0,0115 kgf·m
• Pound force inches to pound force feet
1 lbf.in = 0,083 lbf.ft
• Pound force inches to ounce force inches
1 lbf.in = 16 ozf.in
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