O-IO Maintenance techniques, tools and working facilities
It should be noted that many fasteners, especially Grades 0 through
2, have no distinguishing marks on them. When such is the case, the only
way to determine whether it is standard or metric is to measure the thread
pitch or compare it to a known fastener of the same size.
Standard fasteners are often referred to as SAE, as opposed to metric.
However, it should be noted that SAE technically refers to a non-metric
fine threadfastener only. Coarse thread non-metric fasteners are referred
to as USS sizes.
Since fasteners of the same size (both standard and metric) may have
different strength ratings, be sure to reinstall any bolts, studs or nuts re-
moved from your vehicle in their original locations. Also, when replacing
a fastenerwith a new one, make sure that the new one has a strength rat-
ing equal to or greater than the original.
Tightening sequences and procedures
Most threaded fasteners should be tightened to a specific torque value
(torque is the twisting force applied to a threaded component such as a
nut or bolt). Overtightening the fastener can weaken it and cause it to
break, while undertightening can cause it to eventually come loose. Bolts,
screws and studs, depending on the material they are made of and their
thread diameters, have specific torque values, many of which are noted
in the Specifications at the beginning of each Chapter. Be sure to follow
the torque recommendations cbsely. For fasteners not assigned a specif-
ic torque, a general torque value chart is presented here as a guide. These
torque values are for dry (unlubricated) fasteners threaded into steel or
cast iron (not aluminum). As was previously mentioned, the size and
grade of a fastener determine the amount of torque that can
Metric thread sizes
Ft-lbs
M-6 ................................. 6to9
M-8 ................................. 14to21
M-10 ................................ 28to40
M-12 ................................
5at07i
M-14 ...... .._._r-....*........._ .... 89to140
Pipe thread sizes
l/8 .................................. 5to8
t/4 .................................. 121018
3/8.............*- ................... 22to33
l/2 .................................. 25to35
U.S. thread sizes
i/4-20 .............................. 6to9
5/16-18.. ........................... 12tol8
5116-24 ............................. 14to20
318-16 .............................. 22to32
318-24 .............................. 27to38
7116-14 ............................. 40to55
7/16-20 ............................. 4Oto60
i/2-13 .............................. 55to80
Nm
9toi2
19to28
38 to 54
68 to 96
109to 154
7toio
17to24
3oto44
34 to 47
9toi2
17to24
19to27
30 to 43
37 to 51
55 to 74
55 to 81
75to 108
G-
Standard (SAE and USS) bolt dimensions/grade marks Metric bolt dimensions/grade marks
G Grade marks (bolt length) P Property class [bolt strength)
L Length (in inches)
L Length (in millimeters)
T Thread pitch (number of threads per inch) T Threadpitch (distance between threads in millimeters)
D Nominal diameter (in inches) D Diameter
P-
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