This vehicle provides fastener dimensions using the metric system. Most metric
fasteners are approximate in diameter to equivalent English fasteners. Make replacements
using fasteners of the same nominal diameter, thread pitch, and strength.
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®
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® 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.