Sorry to jump in like this, but I have been reading about single and double DIN and cannot find anywhere that explains what this means. As you can probably guess I am very new to this but also extremely eager to start fiddling....with my latest purchase! Currently I have the original cassette hifi in a box - its about 4 inches tall - which has been replaced by a pioneer clip in system with radio/CD/bluetooth and want to change this for an AUDI RNS-E system (again, slightly mystified as to whether or not this has in-built ability for hands free via bluetooth but that's for another thread). Could someone just clarify the DIN thing for me? Thanks!!!