The AN system has a relatively simple set of conventions for determining size from the "dash number". For example, take AN3 (commonly used for brake lines.) AN3 fittings are designed for 3/16 inch hard line. AN4 fittings are designed for 1/4 inch hard line. In general, take the dash number and use it as the numerator of the fraction (with 16 as the denominator), and normalize it to get the hard line size (that is, for 4AN, the fraction is 4/16, which is 1/4 inch.) The following table shows the common sizes, the associated thread, and the usual automotive applications. There are many more sizes, up to AN20.

AN dash number | Hard Line Size (inches) | Thread | Typical Application |
---|---|---|---|

AN3 | 3/16 | 10-32 | Brakes |

AN4 | 1/4 | 1/4-28 | Clutch |

AN6 | 3/8 | 3/8-24 | Fuel |

AN8 | 1/2 | 1/2-20 | Oil |