Hydraulic Connectors 101

Hydraulic Connectors 101

As the name suggests, hydraulic connectors are used to connect hydraulic circuits by joining two different end terminations together and creating a flow passage to ensure fluid transfer.

Hydraulic connectors can be grouped into three main types:

  • Internal Thread
  • External Thread
  • No Thread

Internal and external threaded connectors are also known as female and male, respectively.

There are many thread standards in the industry primarily based on the country / region of origin. BSP (British Standard Pipe), NPT (National Pipe Tapered), UN (Unified Inch Screw Threads) and Metric to name some of the most common.

To avoid damage to hydraulic systems, selecting the right type of thread is very important.

Common variation in fitting designs are outlined below that is useful in thread identification.

Tapered / Parallel Threads

Some threads have a tapered thread surface, such as BSPT, NPT (denoted by letter T) whereas others are parallel. BSPP, UN are examples for parallel threads.

Tapered threads are designed to seal on the thread surface.

Sealing of Hydraulic Connectors

Along with tapered threads, other sealing methods include:

  • Metal Seal
  • Soft Seal

Metal seal type was developed to maximise sealing of a connector under pressure. Connectors that have this sealing method will include a machined cone seat (convex or concave) that will seal with the corresponding male / female connector.

Common seat angles include:

  • 30° cone seat (BSPP, some Metric fittings)
  • 45° cone seat (SAE fittings)
  • 37° cone seat (JIC fittings)
  • 24° cone seat (Metric fittings)

Some connectors are designed to seal using elastomeric seals, natural or synthetic to prevent leakage. This type of sealing method is common with adaptors intended for port use, where a soft seal on the base of the adaptor will seal with the flat surface of a port.

Soft seal connectors can be seen on the face of male fittings and adaptors (such as ORFS) which will establish a seal with a flat surface on a female fitting of the same size.

Thread Size, Thread Count & Pitch

Thread size is designated by the external major diameter of a thread that can easily be measured using a calliper. The actual measurement is generally slightly lesser than the nominal thread size. Imperial thread sizes are expressed in inches and metric thread sizes in millimetres paired with “M” (e.g. M6 for 6mm).

Thread count (also known as Threads Per Inch – TPI) and pitch are also important factors when identifying threads and are usually stated along with the thread size.

TPI is common with imperial connectors which basically is the number of threads within an inch measured lengthwise.

For metric threads, pitch is used instead which means the distance between two crests of a thread in millimetres.

How to Identify Connectors?
RYCO’s Thread ID Mate application provides an intuitive and simple identification process to help you find detailed information about threads specifications, sizes and more.

Hydraulic threads can be identified using a few simple steps using the Thread ID Kit and RYCO Thread ID Mate application.

  1. Determine the thread type:
    Visually inspect to determine if the connector has and internal or an external thread (if any).
  2. Is the thread tapered or parallel?:
    Tapered threads can be identified by visual inspection or placing a straight surface, such as a ruler, next to the thread to compare the difference in diameter at the shoulder of the fitting to the diameter at the tip.
  3. What type of sealing face / method does the connector have?:
    Check if the connector has a conical sealing face or a flat sealing face, and whether a soft seal is present.
  4. Using Vernier Calipers included within the RYCO Thread ID Kit, measure the outer / inner diameter of the thread:
    Measure the ID / OD of the connector across flats of the Vernier Calipers for better accuracy.
  5. Determine the sealing face seat angle (if any):
    Align the seat gauge of the Thread ID Kit with the seat of the connector and identify the angle that matches with the seat.
  6. Find the pitch / TPI:
    Use the thread pitch gauge to find out the exact pitch / TPI and verify the thread.

RYCO Thread ID Mate offers you a guided, user friendly process to identify connectors quickly and efficiently.

The Thread ID Mate application is available for your Android and iOS devices. That’s thread identification you can keep in your pocket.

Want More Information?

If you would like to know more about hydraulic connectors, contact our RYCO Hydraulics Customer Service team or fill out our contact form.

The three types of hydraulic connectors and their two key functions

The three types of hydraulic connectors and their two key functions

This article is an overview of the theory of hydraulic connectors, the three main types of connectors and the two key functions that all hydraulic connectors must fulfil.

Three Main Types of Hydraulic Connectors

It provides basic information about the three main classes of hydraulic connectors:

  • Tapered Threads
  • Metal seal connectors
  • Soft seal connectors

Two Key Functions of Hydraulic Connectors

It’s important to understand that there are two functions that a hydraulic connector must fulfil:

  • Holding
  • Sealing

Sometimes the holding and sealing functions are provided by the same mechanism, and sometimes by two different parts.

Hose connectors may seem very confusing because of the many different types available.

However, when looking objectively, connectors will always simply do two things. Hold, and seal under pressure.

Development of Hydraulic Connectors

Hydraulic connectors were developed in this order:

  • Tapered threads
  • Metal seal connectors
  • Soft seal connectors

Tapered Threads

Tapered pipe threads were one of the first ways to connect pipes together.

They involve cutting the pipe thread in a tapered manner, so that the diameter of the pipe changes over the length of the fitting.

Tapered Pipe Thread

These kinds of connectors require some form of sealant, either a tape sealant, which can block the pipes, or a chemical sealant, which is preferred.

Tapered pipe threads can also be difficult to orient correctly, leading to poor sealing and leakage.

Tapered threads can also cause damage to other components, including deformation of aluminium and cracking of cast iron, due to the pressure of the steel pipe thread within the component.

They also can’t be connected to hydraulic tubes without soldering or welding of the tube to the part.

Metal Seal Connectors

Metal seal connectors were developed to address some of the limitations of the tapered pipe threads.


A metal seal connector is basically a tapered pipe thread with the addition of a 30 degree machined face, to form a seal.

This feature is generally only in hydraulic systems, because of the high pressures that need to be dealt with.

The addition of the “chamfer” on the face of the thread split the holding and sealing features of the connector.

The thread does the holding and the machined face does the sealing.

This modification also makes the connector easier to orient, better sealing, and eliminates the need for a sealant.

However, metal seal connectors still can’t accept hydraulic tube unless the tube is soldered or welded to it, and they can also have issues with vibration.

The JIC connector is a further development. It has a 37º metal seal and can accept hydraulic hose and tube. BSP Thread, BSPT, BSPP and NPT are common types of threads used in metal seal connectors.

Soft Seal Connectors

Soft seal connectors are the most recent development in the evolution of hydraulic connectors.

They make use of an elastomeric seal – natural or synthetic – to prevent leakage.

Soft Seal Hydraulic Connector

The soft seal also helps connectors resist the effects of vibration, as well as the high-pressures used in many hydraulic systems today.

The seal in a soft seal connector usually takes the form of an O-ring.

Another advantage of soft seal connectors is their rapid assembly, which can be important in high-volume production environments.

The main limitation of soft seal connectors comes from the fact that performance of the o-ring can be affected by temperature and the system fluids, if they’re not compatible with the elastic substance.

Want More Information?

Make sure you select the right hydraulic hose for your next project. Download our 15 Keys To Selecting The Right Hose guide today.