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the shoulder, /x5, extends the NAAN, 12345.

How do I format a shoulder?

Start with your NAAN and decide on a short, fixed extension that you will add to it. The extension should

  • start with one or more lowercase letters,
  • end with a digit (non-zero preferred), and
  • contain no vowels or the letter 'l' (ell).

Some more detail is given in response to the next question.

Why is there no "/" to mark the end of a shoulder?


It's natural to want to visually mark the shoulder's end, but it's prohibited by ARK rules.

Why? If you're interested, the The reason is that adding a "/" after "/x5" makes two false assertions:


In fact, in-house ARK administrators always know where the shoulder ends, provided it was chosen using the "first-digit convention". A primordinal shoulder is a sequence of one or more betanumeric letters characters ending in a digit. This means that the shoulder is all letters (often just one) after the NAAN up to and including the first digit encountered after the NAAN. Another advantage of primordinal shoulders is that there is an infinite number of them possible under any NAAN.


As mentioned, to implement a shoulder under your own NAAN requires no special request. To implement or change a shoulder under a shared NAAN, however, requires getting into the shared NAAN requires shoulders registry, which means filling out an online shoulder form. For security purposes requests are processed manually. Example reasons for a change may include