Mechanix

"Mechanix" is a song by Megadeth, an American thrash metal band. It is the last song from their first studio album, "Killing Is My Business... And Business Is Good!".
The song was written by Dave Mustaine. He made it for Metallica, a band that he was in. After Metallica fired Mustaine, he told the band to not use any of the music that he made, including "Mechanix". Metallica rewrote the song, and named it "The Four Horsemen". They put it on their first album, "Kill 'Em All," in 1983.