brake line question

[CDNRatMan]

 Because a simple reason.....the owner of the company is the dude who measured it and who is going to tell him he was wrong so it has stayed that way forever.........

[greenbarn]

Can someone please answer me a question?  Automotive brake lines are commonly available at several different lengths in each of the standard sizes (3/16", 1/4", and the metric stuff, etc.):

20"
30"
40"
51"
60"

So WHY is the "50" line a 51" line, and not 50 like the rest?  Makes no sense to me.  None of my parts suppliers can answer the question for me.  Must be a reason...