Think of Dura-Ace, 600 and 105 as family names, equivalent to Smith, Jones and Brown. EX, AX, New EX and Ultegra become the equivalent of forenames such as Bob, Jim and Tom. If I just said Smith you wouldn't know if I was referring to Bob Smith or Jim Smith. If I just said Bob, you wouldn't know if I was referring to Bob Smith, Bob Jones or Bob Brown. But if I said Bob Smith you would know exactly whom I'm referring to. The slight difference is that in Shimano's world, the patriarch of the family is only referred to by surname. Also, in the late 1990s one of the families changed their surname (600 became Ultegra). At about the same time big brother took over and did away with forenames, so that we had to start referring to series numbers to distinguish members of a family.

There is no proper way to compress 600 Ultegra, which is why it is often referred to by the nickname of "tri-colour". The only other method to identify it is by the series number which is 6400. So, sometimes you'll see Ultegra 6400 or Shimano 6400.