There are two types of pitch used these days imperial (0.1" = 2.54mm) and metric (2mm).

Most things are 0.1" spaced (MBs, 3.5"HDD, many connectors). However some stuff like 2.5"HDD are 2mm pitch.
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)