Happy National Metal Day! A day to crank the Metal….up to 11! Besides watching all the great new programming on VH1 Classic to celebrate (Metal Evolution Part 1, Behind The Music Remastered: Megadeth, and a new “That Metal Show” with Axl Rose and DJ Ashba of Guns N’ Roses), you may be wondering, just what are the origins of National Metal Day? It actually dates back to the classic 1984 rock movie satire ‘This is Spinal Tap.’ Guitarist Nigel Tufnel (Christopher Guest) is showing his gear to filmmaker Marty DiBergi (actual filmmaker Rob Reiner) and he points out that his Marshall amps don’t go to “10,” like most amplifiers, instead all of the dials go to “11.” It’s the most famous and most used quote from the film. Check out the clip below.

When asked if the amps are louder than those used by other bands, Tufnel says “Well, it’s one louder, isn’t it?” Continuing the gag, DiBergi aks, “Why don’t you make 10 louder, and make that be the top and make that a little louder,” Tufnel pauses like a deer in headlights for a few moments, points to the amp and repeats, “These go to 11.”

To celebrate the legendary film, Amazon.com, iTunes and X-Box are selling ‘This is Spinal Tap’ for $4.99 between now and Monday. In addition, VH1 Classic and PalladiaHD have airing the film throughout the week. In addition, today is also being dubbed Nigel Tufnel Day. You can keep track of the day’s festivities on Twitter and Facebook at the hashtag #GoTo11.

Spinal Tap have released three albums: the 1984 film soundtrack, 1992′s ‘Break Like the Wind’ and 2009′s ‘Back From the Dead.’ In addition, their songs have been included in the video games ‘Guitar Hero 2,’ ‘Rock Band’ and ‘Rock Band 2.’