Friday, July 03, 2009

Bastardized AN fittings - Which AN fitting goes into the hole?

Automotive racing has adopted the aircraft AN fitting technology, bastardized it, and now sent it back into the aircraft industry. I've talked about the differences before in my article "What is the difference between aircraft AN and JIC fittings". The result of this bastardization is confusion and extra expense for the aircraft industry. Let me try to clear up some confusion when it comes to screwing fittings into straight-thread ports.

In non-aircraft applications ports are mostly straight thread "ORB" O-ring Boss. The automtove industry (heck I don't know what to call you guys - "race industry", is that better) has plenty of adapters to adapt AN to the port - pictured below.

There is no AN number for this adapter. It does not exist in the AN series - for good reason - it is not needed in aircraft. In aircraft, the traditional straight threaded boss is called a "AND" port (AND10050 or MS33656) and doesn't require an adapter fitting. This should be the end of the story for us aircraft people but it isn't.

Some automove style components with ORB ports are being used in aircraft. These require the adapter shown above. So now us aircraft people must be able to look at the port and tell what kind it is.

Is it a tapered pipe thread port (NPT), an ORB port or a AND style port? Curse you automotive people for bringing us your ORB crap! NPT is bad enough!

Here is a aircraft brake caliper with a male AN nipple sticking out of the port. It looks like out adapter above. But it's not.

Here is a picture of the entire fitting.

Notice that this is a standard AN fitting. Below is a picture showing how it installs with a boss o'ring.

Simple, just install a a boss O'ring onto the end of a standard AN nipple fitting and screw into the port. You can also use a bulkhead fitting and special nut for high-pressure hydraulic applications.

Here is a picture below.

This port (AND10050 - MS33656) has stronger (greater shear strength) threads (class 3 versus class 2). and can accomidate the extra length of the nipple. It is adaptable to a wide range of AN fittings and pressures.

AN fittings that can be screwed into AND ports are what the drawing calls a Type E style and can be used to seal on the flare OR seal on the nut with an O'ring. Not all AN nipple fittings are Type E. Below is a non-type E fitting.

Notice that there is no nut hex and no circumferal groove above the last thread. If you wish to use a Type E angle fitting then use the bulkhead series with a nut. You can now point the fitting any direction you wish.

What does a AND10050 port look like?

A AND port has a countersink around the top edge forming a 120 degree included angle. This port is also sometimes called a "Military Straight Tread Port". The latest drawing for this port is AS5202.

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