TrailBlazer 2WD L6-4.2L VIN S (2003)
A number marking identifies the OE metric fasteners except cross-recess head screws. The number also indicates the strength of the fastener material.
A Posidrive(r) or Type 1A cross-recess identifies a metric cross-recess screw. For best results, use a Type 1A cross-recess screwdriver, or equivalent,
in Posidrive(r) recess head screws.
GM Engineering Standards and North American Industries have adopted a portion of the ISO-defined standard metric fastener sizes. The purpose was
to reduce the number of fastener sizes used while retaining the best thread qualities in each thread size. For example, the metric M6.0 X 1 screw, with
nearly the same diameter and 25.4 threads per inch replaced the English 1/4-20 and 1/4-28 screws. The thread pitch is midway between the English
coarse and fine thread pitches.
Fastener Strength Identification
The most commonly used metric fastener strength property classes are 9.8 and 10.9. The class identification is embossed on the head of each bolt. The
English, inch strength classes range from grade 2 to grade 8. Radial lines are embossed on the head of each bolt in order to identify the strength class.
The number of lines on the head of the bolt is 2 lines less than the actual grade. For example, a grade 8 bolt will have 6 radial lines on the bolt head.
Some metric nuts are marked with a single digit strength identification number on the nut face.
The correct fasteners are available through GM SPO. Many metric fasteners available in the aftermarket parts channels are designed to metric
standards of countries other than the United States, and may exhibit the following:
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Lower strength
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No numbered head marking system
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Wrong thread pitch
The metric fasteners on GM products are designed to new, international standards. The following are the common sizes and pitches, except for special
applications:
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M6.0 X 1
