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Gordon’s recent post about the strange and elusive numbering scheme for machine screws brought another one to mind, gleaned from Carroll Smith’s Nuts, Bolts, Fasteners and Plumbing Handbook. 37° AN lines are a pretty common sight for lots of high-performance and show vehicles these days, courtesy of their excellent sealing performance and reusability. But how do you plan line sizes without really knowing the dimensions of a given fitting and its hoses?

Turns out, it’s pretty simple. The lines are sized with labels like -3AN up to around -20AN (standards up to -32AN exist, but the fittings are very rare). To determine the hose inner diameter for a specific AN size, just multiply the prefix by 1/16″. For instance, -10AN:

10(1/16″) = 10/16″ = 5/8″ inner diameter.

Thread sizes and hex dimensions are also standardized, as Wikipedia and Powerhouse’s AN wrench selection show us.

AN Thread Specs [Wikipedia]
AN Hex Wrenches [Powerhouse]

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3 Responses to AN Numbering Scheme

  1. Ted says:

    One minor caveat, the actual I.D. for stainless braided teflon (the stuff used for crafting your own flexible brake and clutch lines) is usually off by one dash size or 1/16″, ie -3 = 1/8″ I.D., -4 = 3/16″ I.D. for some strange reason I’ve never understood.

    All other hoses, and tubes for that matter, are as as described in the post, -1 = 1/16″.


  2. rob says:

    I love these things they cost a fortune
    but having all of your fittings standardized is nice
    when you have a twin turbo setup on a small motor in a tight space
    not having to guess at fitting sizes is huge
    I use -3 an for my oil and brake brake lines
    and -6 for my fuel

  3. _Jon says:

    I have almost $500 worth of the stuff on just my fuel lines. That was painful.

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