How to determine proper hydraulic hose fittings?
Many devices and tools now have their own unique sealing and connection methods.
Both the thread and sealing method vary depending on the equipment’s design and characteristics.
Hydraulic hose fittings are used to connect two fluid ports to prevent leakage under high-pressure transportation.
The threads and shapes of hydraulic hose fittings are very similar. This can increase the difficulty of selecting the appropriate hydraulic hose fitting when purchasing and repairing equipment.
This article will introduce you to the basics of hydraulic fittings, helping you choose the best hose fitting and ensuring that the hydraulic hose fitting meets the stringent requirements of your application.
5-step procedure to identify hydraulic hose fittings
Two Types of Fittings
Hydraulic hose fittings can be mainly divided into two types. One is a crimped fitting, also known as a permanent fitting. The other is a reusable fitting, also called a returnable fitting.
Crimped fittings are connected to the hose end using a crimping machine, securing the hydraulic hose to the hydraulic system. In most cases, crimped hydraulic hoses are used.
Crimped fittings are simple in structure, easy to install, and require no additional glue or seals. They ensure a tight, seamless connection between the hose and other equipment, minimizing the risk of leakage. Furthermore, crimped fittings use high-strength materials, can withstand higher pressures, and have a longer service life. Therefore, they are widely used.
Reusable fittings are often considered the old-school option. Their safety and sealing performance are not as good as crimped fittings.
If you are unsure about the type of fitting for older equipment but need to replace a fitting, you can determine the type of fitting by considering these two aspects: First, consider whether crimping tools were used during installation. Also, check the connection method of the fitting. The returnable type of fittings is installed on the hose with the help of screwing.
crimped fitting
reusable fitting
8 Types of Fitting Connections
There are many types of end connections for fittings. You can choose the appropriate hose and fitting based on the connection type and specified end. For example, a 4-bolt flange is one of the connection types. It is suitable for both metric and BSPP (British Standard Pipe Parallel Thread) 60⁰ cone tube coupling (hose connection).
Below is a quick overview table of threaded connections and different hose connection methods.
| Port Connections | Hose Connections |
| NPT / NPTF | 37° Flare |
| BSPT (JIS-PT) | 30° Flare (Metric) |
| Metric Taper | 45° Flare |
| SAE Straight Thread | 24° Flareless (SAE) |
| ISO 6149 | 24° Flareless (DIN) |
| JIS-B2351 | 30° Flare (BSPP) |
| BSPP (JIS-PF) | 60° NPSM Swivel |
| DIN Metric | O-Ring Face Seal (ORFS) |
Three Types of Sealing
To distinguish between different types of joints, you also need to differentiate their sealing methods. The following will introduce three common sealing methods: O-ring sealing seal, Seat Angle seal, and Tapered Threads seal.
O-ring sealing
The main purpose of the O-ring sealing technique is to provide the seal itself. Speaking about sub-sorts of O-ring couplings, it is worth mentioning the following three types:
O-ring boss: This type of connector is also called ORB fittings. ORB fittings are part of a class of fittings that use O-rings for sealing, providing a leak-free connection. The “Boss” part refers to the specific type of machined surface on the fitting that is designed to hold an O-ring for sealing. ORB fittings are used primarily in systems that require a strong and reliable seal for fluids under pressure
Flat face O-ring seal (Female): It is often called ORFS fittings. These pieces have a smooth, flat surface that the male fitting presses against. When they come together, the O-Ring gets squished, creating a super-strong seal.
O-ring flange: A flange seal is a type of O-ring seal that uses a specific installation position.
Mated Angle
The sealing technique is based on two types of threads: straight and parallel. There are male and female units that form the thread itself. Here are the graphics that describes all the possible variants of the mated-angle type of threads.
| Seat Angle | Standard |
| 30° | BSPP / Metric |
| 37° | SAE JIC |
| 45° | SAE / Automotive |
Tapered Threads
This technique is notable with inside-thread female items and outside-thread male ones. The graphical description of the NPT (National Pipe Tapered) and BSPT (British Standard Pipe Tapered) models are presented below:
| Thread | Tapered Angle |
| National Pipe Tapered Fuel (NPTF) | 60° |
| National Pipe Tapered / Straight Mechanical(NPT / NPSM) | 60° |
| British Standard Pipe Tapered(BSPT) | 55° |
Identify the Tread Size
You will need to use a thread gauge to begin taking measurements. Please note that threads are measured in inches. The images below show both tapered and hexagonal threads. These charts can be used to easily determine the thread specification.
Male Pipe Thread Sizes
| Nominal Size (Inside Diameter) | Actual OD | Threads per Inch | Length of Engagement (Hand Tight) | Hand Tight Turns | Wrench Makeup Turns | Length of Effective Thread |
| 1/16 | 0.3125 | 27 | 0.16 | — | — | 0.2611 |
| 1/8 | 0.405 | 27 | 0.18 | 4½ | 2½ | 0.26 |
| 1/4 | 0.54 | 18 | 0.2 | 4 | 3 | 0.401 |
| 3/8 | 0.675 | 18 | 0.24 | 4½ | 3 | 0.408 |
| 1/2 | 0.84 | 14 | 0.32 | 4½ | 3 | 0.534 |
| 3/4 | 1.05 | 14 | 0.34 | 4½ | 3 | 0.546 |
| 1 | 1.315 | 11.5 | 0.4 | 4½ | 3¼ | 0.682 |
| 1¼ | 1.66 | 11.5 | 0.42 | 4½ | 3¼ | 0.707 |
| 1½ | 1.9 | 11.5 | 0.42 | 4½ | 3¼ | 0.724 |
| 2 | 2.375 | 11.5 | 0.436 | 5 | 3 | 0.756 |
| 2½ | 2.875 | 8 | 0.682 | 5½ | 3 | 1.136 |
| 3 | 3.5 | 8 | 0.766 | 6 | 3 | 1.2 |
| 3½ | 4 | 8 | 0.821 | 6½ | 3½ | 1.25 |
| 4 | 4.5 | 8 | 0.844 | 6¾ | 3½ | 1.3 |
| 5 | 5.563 | 8 | 0.937 | 7½ | 3¾ | 1.4063 |
Nut and Nipple Hex Sizes
| Size | Width Across Flats (F) | Width Across Corners (G) | Thickness of Hex Nuts (H) | ||||||
| Basic | Max | Min | Max | Min | Baslc | Max | Min | ||
| 1/4 | 0.2500 | 7/16 | 0.438 | 0.428 | 0.505 | 0.488 | 7/32 | 0.226 | 0.212 |
| 5/16 | 0.3125 | 1/2 | 0.500 | 0.489 | 0.577 | 0.557 | 17/64 | 0.273 | 0.258 |
| 3/8 | 0.3750 | 9/16 | 0.562 | 0.551 | 0.650 | 0.628 | 21/64 | 0.337 | 0.32 |
| 7/16 | 0.4375 | 11/16 | 0.688 | 0.675 | 0.794 | 0.768 | 3/8 | 0.335 | 0.365 |
| 1/2 | 0.5000 | 3/4 | 0.750 | 0.736 | 0.866 | 0.840 | 7/16 | 0.448 | 0.427 |
| 9/16 | 0.5625 | 7/8 | 0.875 | 0.861 | 1.010 | 0.982 | 31/64 | 0.496 | 0.473 |
| 5/8 | 0.6250 | 15/16 | 0.938 | 0.922 | 1.083 | 1.051 | 35/64 | 0.559 | 0.535 |
| 3/4 | 0.7500 | 1-1/8 | 1.125 | 1.088 | 1.299 | 1.240 | 41/64 | 0.665 | 0.617 |
| 7/8 | 0.8750 | 1-5/16 | 1.312 | 1.269 | 1.516 | 1.447 | 3/4 | 0.776 | 0.724 |
| 1 | 1.0000 | 1-1/2 | 1.500 | 1.450 | 1.732 | 1.653 | 55/64 | 0.887 | 0.831 |
| 1-1/8 | 1.1250 | 1-11/16 | 1.688 | 1.631 | 1.949 | 1.859 | 31/32 | 0.999 | 0.939 |
| 1-1/4 | 1.2500 | 1-7/8 | 1.875 | 1.812 | 2.165 | 2.066 | 1-1/16 | 1.094 | 1.030 |
| 1-3/8 | 1.3750 | 2-1/16 | 2.062 | 1.994 | 2.382 | 2.273 | 1-11/64 | 1.206 | 1.138 |
| 1-1/2 | 1.5000 | 2-1/4 | 2.250 | 2.175 | 2.598 | 2.480 | 1-9/32 | 1.317 | 1.245 |
| 1-5/8 | 1.6250 | 2-7/16 | 2.438 | 2.356 | 2.815 | 2.686 | 1-25/64 | 1.429 | 1.353 |
| 1-3/4 | 1.7500 | 2-5/8 | 2.625 | 2.538 | 3.031 | 2.893 | 1-1/2 | 1.54 | 1.46 |
| 2 | 2.0000 | 3 | 3.000 | 2.900 | 3.464 | 3.306 | 1-23/32 | 1.763 | 1.675 |
| 2-1/4 | 2.2500 | 3-3/8 | 3.375 | 3.263 | 3.897 | 3.719 | 1-15/16 | 1.986 | 1.89 |
| 2-1/2 | 2.5000 | 3-3/4 | 3.750 | 3.625 | 4.330 | 4.133 | 1-23/32 | 2.209 | 2.105 |
| 2-3/4 | 2.7500 | 4-1/8 | 4.125 | 3.988 | 4.763 | 4.456 | 2-3/8 | 2.431 | 2.319 |
| 3 | 3.0000 | 4-1/2 | 4.500 | 4.350 | 5.196 | 4.959 | 2-19/32 | 2.654 | 2.534 |