The following flare fittings are similar, but not equivalent:

• AC (Air Corp Standard) also called Parker Triple Fitting (NOT Triple-Lok)
• AN (Air Force - Navy Aeronautical Standard)
• AND (Air Force - Navy Aeronautical Design Standard)
• AS (Aerospace Standard)
• MS (Military Standard)
• JIC (Joint Industry Council)
• SAE 37° also called Parker Triple-Lok
• ISO 8434 (1986), ISO 8434-2 (1996)
• SAE 45°

AC (Air Corp)

The AC flare fittings were developed for the aviation industry in the 1930s, and have long since been superceded by AN.  Today, it is rare that you will come across one of these fittings.  AC fittings use a 30° flare angle, and they are most readily recognizable by a very short or non-existent straight section between the top of the thread (on the male fitting) and the major diameter of the flare.  Most flare fittings of the other types have a non-threaded section at the base of the flare.

Note that the AC were talking about here has nothing to do with air conditioning.  It is possible that some people may use the term "AC Flare" to refer to the SAE 45° fittings discussed below.

AN, AND, MS, AS

AN / AND fittings have a 37° flare angle and use a class 3A/3B thread, which is a close tolerance, radiused root thread.  These fittings have traditionally been available in aluminum, carbon steel, stainless steel, and titanium.

AN / AND fittings remain in prevalent use today, and they may alternatively be designated with an MS number, which are generally directly cross-referenced replacement fittings (functionally equivalent).  For instance, an AN815 is equivalent to an MS24392.  MS, however, is a very broad standard covering all kinds of hardware, and is not limited to AN fluid couplings.

The AN and MS designations for many fittings are being superceded with AS (Aerospace Standard).

In general, there appears to be a trend away from flared tubing in favor of compression type fittings, probably due to the fact that flares require greater special attention to craftsmanship (and more time) in assembly

JIC, SAE 37°, ISO 8434, Parker Triple-Lok

When someone says it's a JIC fitting, this is generally what they are talking about.  This fitting is the general industrial adaptation of the AN fitting.  These fittings have a 37° flare angle and use a class 2A/2B thread, which is a standard tolerance industrial thread with normal trapezoidal root truncation.  These fittings have traditionally been available in carbon steel, stainless steel, and brass. Some of these fittings may conform to MIL-F-18866 and/or SAE-J514.

SAE 45°

The SAE 45° fitting is typically used for low pressure applications, usually with soft copper or soft aluminum tubing, which flares easily to the 45° angle.  These fittings are easily recognized by placing them on a square, or by placing two males flare-against-flare at right angles, and observing the 90 degree included flare angle,  The 45° flare fitting is the one you are most likely to run across at your local hardware store.  They are commonly found in use in the following applications:

• refrigerant lines
• fuel lines
• natural gas appliance hookups
• ice maker connections
• domestic water systems in motor homes

JIC 37° / SAE 45° Dual Angle Seat

There are some fittings made which can be screwed onto either a 37° or a 45° fitting.  The dual angle flare seat is apparent.  Obviously, this is a kind of bastard fitting, and should not be selected as a primary style in the design of any hydraulic system, though they surely come in handy at times.