M42

M42 or M-42 may refer to:

In science:

• Messier 42 (M42), a nebula also called the Orion Nebula
• The 42nd known Mersenne prime

In transportation:

• M-42 (Michigan highway), a state highway in Michigan
• M42 motorway, a motorway in the United Kingdom
• BMW M42, a 1989 automobile piston engine
• Grand Central Terminal M42, a World War II era sub-basement and power station beneath New Yorks Grand Central Station train terminal

In photography:

• M42 lens mount, a standard for cameras

In firearms and military equipment:

• M42 Duster, a United States Army self-propelled anti-aircraft gun
• M42 (gas mask), a United States military gas mask
• M/42 (bicycle), a Swedish military bicycle
• 45 mm anti-tank gun M1942 (M-42), a Soviet anti-tank gun
• M42 Stahlhelm, a type of German WWII helmet
• M42, a Smith & Wesson hammerless revolver
• M42 United Defense submacine gun, an American weapon used in World War II

In manufacturing:

• M42 grade of high speed steel with cobalt

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