What is the difference between an M35, M40 and M42 helmet?
An M35 helmet has a rolled rim around the edge of it. The air-vents are actually pressed-in grommet inserts. The M40 helmet substituted stamped air-vents for the pressed grommet air-vents but retained the rolled rim. The M42 has an unrolled rim to further cut time and machinery needs in helmet production. (See illustrations below) The M35 was produced until mid-1940 when the helmet manufacturers switched their tooling to produce the M40 version. During 1942 the specifications for a rolled rim were eliminated and manufacturers began switching to the M42 version.
