Viewing a thread - Can someone explain to me hydraulic fitting sizes....

WiReading through this whole thread shows the confusion that exists mainly due to different industries slang terms.

Not to beat the dead horse, but some of this will be reorganized repeats.

Lets start with sizing.

The "dash" sizing is what you are referring to and is what many fittings and hoses go by. It came from the US military after the Aeronautical and Navy agreed on a standard. The standard was and still is called "AN". You won't find AN fittings on your farm though, they are aluminum fittings, generally anodized and used with braided stainless or kevlar hose as well as forms of hard tubing. It is used extensively in aviation and is the choice for almost every motorsport due to its serviceability. Assembling AN hoses is a lengthier process than whipping up a hydraulic hose though.

The AN standard used a 37* Flare that created the seal. Dash sizing is easy to figure out, its simply in 1/16ths. I actually prefer the dash system anyways. Much easier to hear dash 4 or Dash 12 over the than it is to try and distinguish between 1/4 and 3/4. I assume this could partially be why the military chose it.

The fittings we all have on our equipment use the same threads, the same sizing and the same 37* flare as their AN counterparts but are built much heavier. (AN fittings and hose typically aren't rated much over 300psi whereas JIC is rated up to 5,000psi )

JIC stands for Joint Industry Council. Essentially, awhile back, everybody got together and agreed on that style fitting for use in many things, in an effort to make things more "standard".


Below are the most common Hydraulic Fitting styles you will find on a North American machine.

NPT: National Pipe Thread. Known by many names, but the key features are a tapered thread that relys on thread distortion to form the seal. On the newer "improved NPT" fittings the "thread sealer" is acting more as a lube than anything to encourage the threads to deform to each other without error. These fittings generally have a 30* internal taper as well right at the edge when using true Hydraulic fittings. Many people will use black pipe or galvanized pipe instead which can lead to poor results, or expensive repairs. Hydraulic pipe thread pieces are made out of steel. NPT's upside is that it is very simple, very cheap and very common. The downside is that it is not very serviceable. Often times the fittings are rigid making removal and installation difficult. In addition the fittings wear out quickly and loose their ability to seal. They take much more torque to achieve a good seal and take much more time to install due to the need to physically distort the threads.

37* JIC: Probably the most common right alongside NPT. As explained earlier, utilizes male/female 37* flares to create the seal. You will generally find that most hard steel lines have JIC threads, some older ones have NPT though. JIC's advantage's include easier installation due to them generally having a swivel at both ends and being able to run the fitting on the majority of the way by hand. JIC is not very expensive compared to other models but can be considerably higher than NPT. The downside to JIC is that it is very sensitive to overtightening, which many people fail to observe. Most are so used to cranking on NPT fittings that they feel the need to put their weight into a JIC fitting. Proper torques on these fittings are very very low. So low they make special wrenches so you don't over do it. Overtightening will slowly ruin the flare and the fitting becomes useless. There are inserts available that act as a sealing washer though.

45* SAE: This fitting is similar to the 37* in many ways. However it is rarely used in hydraulic systems. Generally it is reserved for Fuel, Oil, and Air systems on vehicles. Semis are full of these fittings. Most are Brass and running under lower pressures. Don't need to worry about it much for hydraulics as you will rarely run into one if ever.

STORB: Straight Thread O-Ring Boss. Sometimes just called O-ring boss, sometimes SAE O-ring, other times O-ring port fittings, and a number of other combonations. The main thing to remember are the key aspects, SAE straight threads, O ring seal on threads. These fittings rely on an O-ring seated in a boss above the threads to seal things up. They are generally used as adapters for going into hydraulic rams, motors, distribution blocks, etc etc. Its not too often that they are crimped directly onto the hose, but there are some cases where this is true. The advantages to STORB are that it is serviceable. O-ring kits are available with the proper o-rings. Another big advantage is that 90* fittings can be oriented in the direction that they are needed if the proper fitting is chosen. Installation is quick, but again these generally are installed to adapt a valve block to JIC or ORFS fitting on the hose.

ORFS: O-Ring Face Seal. These fittins are also called O-Ring Seal, when referring to the STORB fittings O-Ring Boss is generally used. Seal is on the face, Boss is on the threads. Easy to remember. These fittings also have straight threads, but utilize an o-ring mounted in the face of the male fittings to do the sealing. The Females are almost all swivel and have a flat face inside them that mates up to the o-ring to seal. These are becoming more and more popular. Construction equipment is almost exclusively using this style along with split flange. Advantages to this style are its durability. Generally rated for double what JIC can handle, these fittings seal very well. They are serviceable too. Kits are available with the proper O-rings. They install very nicely and are more forgiving if over tightened. Disadvantages to this style are prices and availability. I stock all of them in our shop, but most of the dealers and parts stores around here that do hoses do not stock a full line except for the Parker Store and NAPA. They are the most money out of any of the fittings, mostly due to supply and demand though. These are by far my favorite style of fitting to use if possible.

Code 61/62: These are generally called "Split Flange" fittings because they incorporate two flanges that clamp the fitting into place. Most often these are found on pumps and some large hydraulic rams. Think of the ORFS face and magnify it. These fittings essentially use the same concept just use two flanges to mount them instead of a threaded nut. Advantages are that they can be put in very tight spaces, easy to mount to pumps and such, serviceable, easy to install as well. They are relatively cheap but again, supply demand plays a role which keeps the price up.

Inverted Male Flare: This is one you will only find in power steering and hydraulic brake systems generally. It uses a pipe with an internal flare and a nut that presses on the out edges of the flare to seat it into the port it is going into.



Hopefully that clears up the styles of fittings somewhat. If you need charts on how to measure them to make sure you get the right one there are plenty all over the internet to download, otherwise let me know and Ill post one.


As important as the fittings is the hose. There are many to choose from but making sure you have the proper hose is key. For most farmers purposes 2 wire does most of it. Higher pressure components though will used 4 wire hose and such. Then there are other special hoses too that are sometimes used. Its important to note that as you change hose types, different fittings become incompatible. So if you are mad at the hose guy because he has the fitting you need but he says it wont work with the hose you need, that is why.

Same applies for crimping ends onto old hoses. Most places won't do it, and its in your best insterest not to. If you have to get going and the proper stuff is not available you can try it, but its just temporary. The major issue is incompatibility between hoses and ends. If you have eaton hose, you use eaton ends, etc. The crimp dimensions are very precise, over crimping or under crimping can case more headaches than it is worth. In addition, the hose has already been compromised by a hole in it somewhere which has exposed the internal steel to the elements and started deteriorating it. Its always cheapest to make a new hose in the long run.

Clean hoses count too. Best to use a scallop blade or hydraulic hose saw for cutting the hose as it will leave less debris behind. The only way to truely get the hose cleaned out though is to use a foam gun which shoots a foam pellet through the hose to scrape everything out of it. Not many shops have these. They run $1,000+. The CAT shops do have them though.

Don't forget to orientate your ends correctly too. Know a lot of guys who just crimp two 90's on and say its fine because the hose is long enough they can "twist/flex" it enough to get it one. In reality what you are doing is putting the hose in a pre-loaded state versus relaxed, which leads to premature failure.

Good name brands of Hoses and Fittings are Eaton Weatherhead, Parker, and Gates.

If you can make all your own hoses, its nice. Maybe do them for the neighborhood? Usually what we end up doing. I stock every Eaton Weatherhead fitting style in their "U" series and 100+' of H245 Hose in the following sizes, 04,06,08,10,12 & 16. It ends up being around 300 or so fittings. Also stock 50-100' of 6 different sizes of Kevlar wrap as well as the Oetiker Clamps for clamping it on cleanly. Overall, this inventory ended up costing between 15,000-20,000. Our supplier has a good deal that as long as you buy from them, you get to keep a crimper, the needed dies and as many storage cabinets as needed for a small refundable deposit. I acquired them over the past couple years. Many of them are not on any of our machines, but maybe someday will be. There is nothing I hate more than to have someone come here for a hose and I have to say that we dont have the right ends. In addition, the amount of time and money that setup saves us year round is immense. Its very nice for customizing/building equipment as well.

For typical higher pressure (3,000 psi or more) hydraulic system applications in rigid fluid lines corrosion resistant fittings are annealed CRES 304, CRES 321 or CRES 304-1/8-hard. The higher tensile strength of these stainless fittings and thin walled tubing provides a final installation weight that is only slightly more than thicker wall aluminum alloy tubing, yet allows for greater corrosion resistance under higher pressures. Steel lines are used in landing gear and wheel well areas because of the risk of foreign object damage (FOD), where ground debris such as gravel or even ice can easily be kicked up into these critical safety zones.

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Due to the high stress on aircraft brakes there is a potential for failure if the wrong hardware is used. It is imperative to ensure the condition of all threads and O-ring seating areas are properly machined into the housing along with the threads of the fittings which seat into the housing ports.

Seamless stainless steel tubing is frequently used in hydraulic systems. Seamless tube can be bent
to shape much more easily than steal pipe, withstands higher pressures and connects more securely with the right fittings. It’s the same with hydraulic hose. The hose is only as good as the connection.
It is important to use high quality tubing or hose and fittings to ensure an effective seal. That’s why components that have been ASC and Nadcap certified are often used by OEMs of commercial, industrial and heavy equipment and by maintenance engineers in manufacturing plants and those who maintain earth moving equipment and machinery.

It is common for manufacturers of fluid system components that are qualified to supply low and
high pressure fittings and adapters for the aerospace and military market to also provide these same products for critical applications in industrial, construction and commercial equipment. Components that meet these stringent requirements are often used by some of the top OEMs and maintenance crews in the manufacturing and repair of equipment from off-road and heavy machinery to CNC milling machines. Any equipment or machinery that must withstand harsh environments or frequent actuation can benefit from using military grade materials to ensure top performance and long service life.

It is important to note that though some fittings may look identical, no two fittings are the same. The AN (Army-Navy) military standard calls for tighter tolerances and defines all fitting types, whereas the JIC (Joint Industry Council) uses AN specifications as the base line for their own standards and covers fewer sizes. Though JIC fittings and adapters are very similar to the same size AN, JIC tolerances are more lenient than the comparable AN component. Military grade AN fittings are the best choice for critical applications because they provide a superior sealing surface and have tighter dimensional tolerances than JIC fittings. That being said, JIC components are still a reliable choice for less critical applications.

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NOTE: It is important to not combine fittings and tubing made of different material in order to avoid corrosion caused by dissimilar metals.

These fittings incorporate a port connection as recommended by the National Fire Protection Association (N.F.P.A.) for leak prevention in medium and high pressure hydraulic systems. The male connection is a straight thread with an O-ring. The female port has a straight thread and a machined surface to provide a smooth, flat, accurately located surface (minimum spotface), along with a chamfer where the O-ring seats. It seals when the O-ring is compressed into the chamfer when mating the male connection.

The O-ring in an O-ring boss fitting seats between the threads and wrench flats, and is positioned around the OD of the male end of the fitting. This allows for a leak-tight seal which is seated against the
female port.

O-ring boss fittings are either adjustable or non-adjustable. Adjustable O-ring fittings are typically elbows or tees that are installed in a fixed direction. Non-adjustable O-ring fittings are usually plugs and basic connectors that are fitted into a port without the need for alignment.

Proper tube, hose and fitting installations in aircraft and other military equipment are some of the
most critical applications. They are also critical in heavy machinery, cranes (overhead and boom),
earth moving equipment and other construction and general industrial equipment. The appropriate connection and torque are imperative. Metal-to-metal contact between the fitting and flare is necessary to provide the proper seal. In this respect, never apply pipe compound or sealing tape to the faces of the fittings or flare. It is important that the line assembly is in alignment before applying the designated torque to the fittings. 

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