The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 55.2-59 Power Steering and AC lines

e015475 · 09-12-2019, 12:06 PM

From the interwebs -

"JIC fittings are dimensionally identical to AN (Army-Navy) fittings, but are produced to less exacting tolerances and are generally less costly."

My experience with true AN fittings is that most are made out of aluminum and intended for aircraft use. For safety, the thread form (or class of fit) is controlled to tighter tolerances on AN, mostly at the thread root radius to reduce stress risers in the part when it is tightened.

For a hot rod, there's no practical difference between AN and JIC except the price. A steel JIC fitting with a poorer thread class is still stronger it's aluminum AN equivalent.

Where you can get into trouble is buying AN aluminum fittings for automotive use that are advertised as AN, but in reality are JIC. The root radius and thread are not tightly controlled and stress risers can cause them to break in severe applications, and I'd call an automotive power steering system operating at 900-1000 psi 'severe'.

If you absolutely love blue anodized fittings, buy the 'real' ones from Aircraft Spruce.

For either JIC or AN, sizes are usually expressed as 'dash numbers' because that's the way they were identified in a MIL spec back before WW2. For instance, a AN tube nut in 3/8" size would be a 'AN818-6' , or in common parlance, just a 'dash 6 tube nut'.

All 'dash numbers' for JIC or AN fittings are just increments of 1/16th of an inch. So a -6 fitting is for a 3/8" tube (measured on the OD of the tube)

I plumbed all my hydraulic lines for the hydroboost in -6 JIC, which is 3/8", except for the reservoir to the Saginaw TC pump, which is a -12 or 3/4"

09-12-2019, 12:06 PM	#23
e015475 Registered User Join Date: Nov 2013 Location: Show Low, Arizona Posts: 761	Re: Power Steering and AC lines From the interwebs - "JIC fittings are dimensionally identical to AN (Army-Navy) fittings, but are produced to less exacting tolerances and are generally less costly." My experience with true AN fittings is that most are made out of aluminum and intended for aircraft use. For safety, the thread form (or class of fit) is controlled to tighter tolerances on AN, mostly at the thread root radius to reduce stress risers in the part when it is tightened. For a hot rod, there's no practical difference between AN and JIC except the price. A steel JIC fitting with a poorer thread class is still stronger it's aluminum AN equivalent. Where you can get into trouble is buying AN aluminum fittings for automotive use that are advertised as AN, but in reality are JIC. The root radius and thread are not tightly controlled and stress risers can cause them to break in severe applications, and I'd call an automotive power steering system operating at 900-1000 psi 'severe'. If you absolutely love blue anodized fittings, buy the 'real' ones from Aircraft Spruce. For either JIC or AN, sizes are usually expressed as 'dash numbers' because that's the way they were identified in a MIL spec back before WW2. For instance, a AN tube nut in 3/8" size would be a 'AN818-6' , or in common parlance, just a 'dash 6 tube nut'. All 'dash numbers' for JIC or AN fittings are just increments of 1/16th of an inch. So a -6 fitting is for a 3/8" tube (measured on the OD of the tube) I plumbed all my hydraulic lines for the hydroboost in -6 JIC, which is 3/8", except for the reservoir to the Saginaw TC pump, which is a -12 or 3/4"