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.
3.
Tightening torque (Cs)
Torque values are listed in newtonmetre (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.



Conversion
table
The internationally accepted unit is the newtonmetre (N·m)


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

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



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

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



