Though the mockumentary may be a bit familiar and perhaps even overdone these days, when This is Spinal Tap premiered in 1984, the entire concept was still revelatory and new. Spinal Tap may not be the first of its kind-it is predated by the Monty Python Beatles-spoof The Rutles and Woody Allen’s Zelig-but Rob Reiner’s brilliant send-up of a British rockstars set the bar for the genre very, very high. Say at about 11 on a scale of 1 to 10. As the band, known for hits like “Big Bottom” and “Sex Farm,” travels across America to promote their new album “Smell the Glove,” they are forced to confront the fact that they are quickly fading into obscurity. After a string of canceled gigs, a radio announcer who places them in the “Where are they now?” file, and the unwanted arrival of the lead singer’s girlfriend, the boys stop at a roadside diner to discuss various ways to re-enliven their tour and gain a new fan base. Their ideas include introducing new costumes based on the signs of the zodiac and more memorably, bringing back their old number Stonehenge, which features a giant replica of the famous monument descending onto the stage as a group of dwarves merrily dance around it. Unfortunately, when Nigel draws up the dimensions on a napkin, he confuses inches with feet and the resulting replica is no bigger than the dancing dwarves. The scene was filmed at Season’s restaurant in Cleveland and has since closed.