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GENERAL INFORMATION
OA-5
POSlDRlV
SCREW HEAD
IDENTIFICATION MARKS (4)
Fig.
OA-1 1
Cross Recess Screw
and 25.4 threads per inch. The thread pitch is in between the
customary coarse and fine thread pitches.
Metric and customary thread notation differ slightly.
The difference is illustrated in Fig. OA-12.
FASTENER STRENGTH
IDENTIFICATION
Most commonly used metric fastener strength property
classes are 9.8 and 10.9 with the class identification embossed
on the head of each bolt. Customary (inch) strength classes
range from grade 2 to 8 with radial line identification
embossed on each bolt head. Markings correspond to two
lines less than the actual grade (i.e., grade 7 bolt will exhibit
5 embossed radial lines on the bolt head). Some metric nuts
will be marked with single digit strength identification
numbers on the nut face. Fig. OA-13 illustrates the different
strength markings.
When replacing metric fasteners, be carful to use bolts
and nuts of the same strength or greater than the original
fasteners (the same number marking or higher). It is likewise
important to select replacement fasteners of the correct size.
Correct replacement bolts and nuts are available through
General Motors Parts Division. Many metric fasteners
available in the after-market parts channels were designed to
metric standards of countries other than the United States,
and may be of a lower strength, may not have the numbered
head marking system, and may be of a different thread pitch.
The metric fasteners used on these products are designed to
new, international
standards that may not yet be
manufactured by some non-domestic bolt and nut suppliers.
In general, except for special applications, the common sizes
and pitches are:
CUSTOMARY
METRIC
M6.3
X
1
1
THREAD M W O R
NUMBER OF THREADS
THREAD MAJOR DIAMETER
DISTANCE BETWEEN
DIAMETER I N INCHES
PER INCH
I N MlLLlMETRES
THREADS I N MlLLlMETRES
s
I
4997
Fig.
OA-12
Thread Notation
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