When selecting a fitting for a hose, a piping system, or a hydraulic system, several factors must be taken into account. In addition to the size, you need to check, among other things, the thread type, sealing method, fitting design, and whether the connection is fixed or flexible.
In the table below, you'll find common abbreviations used for hose fittings, hydraulic fittings, and pipe fittings. These abbreviations help you identify the fitting's design and the standard or sealing principle it uses.
Common designations for coupling types
| Abbreviation | Meaning | Explanation |
|---|---|---|
| IR | Internally threaded movable | An internally threaded connection that can rotate during installation. |
| UF | Externally threaded, fixed | An externally threaded connection that is fixed relative to the coupling body. |
| IF | Internally threaded fixed | An internally threaded connection without a movable nut. |
| R | Pipe Thread, BSP | BSP pipe thread. Check whether the connection is parallel or tapered. |
| KR | Tapered pipe thread, BSPT | Tapered BSP thread that seals at the thread joint using a suitable sealing material. |
| NPTF | American tapered pipe thread | Tapered American pipe thread with a 60-degree thread angle. |
| JIC | UNF thread and 74° sealing surface | Coupling with a 37° cone on each side, resulting in a total sealing angle of 74°. |
| M | Metric thread | A thread where the diameter and pitch are specified in millimeters, for example, M18 × 1.5. |
| SKL | Cutting coupling, pressure class L | Light-duty shear coupling. |
| SKS | Cutting coupling, pressure class S | Heavy-duty shear coupling. |
| RSL | Pipe coupling, pressure class L | Pipe fitting designed for the lightweight series. |
| RSS | Pipe fitting, pressure class S | Pipe support designed for heavy-duty applications. |
| DKO-L | Metric thread, 24° cone, and O-ring, pressure class L | Seal with a 24° cone and O-ring in the light-duty series. |
| DKO-S | Metric thread, 24° cone, and O-ring, pressure class S | Seal with a 24° cone and a heavy-duty O-ring. |
How do you identify the correct connection?
To identify a connection, you usually need to check:
- internal or external thread
- fixed or movable design
- thread diameter
- thread pitch
- parallel or tapered thread
- sealing surface and cone angle
- any O-ring
- light or heavy print run
A caliper and a thread gauge can be used to check the dimensions and pitch. Then compare the measurements with the product's technical documentation.
What is the difference between a fixed and a variable connection?
A fixed coupling does not rotate relative to the coupling body. Therefore, during installation, the entire hose or component often needs to be rotated.
A swivel coupling, on the other hand, has a nut or connector that can rotate. This makes installation easier and reduces the risk of the hose twisting or being subjected to improper stress.
What is the difference between internal and external threads?
An internal thread is located on the inside of a nut or coupling and connects to an external thread.
There is an external thread on the outside of the coupling. For the connection to fit, the thread type, size, and pitch must all match.
What is the difference between BSP, BSPT, and NPTF?
BSP is a British threading system used in many European installations. BSP threads can be either parallel or tapered.
BSPT is the tapered version of BSP. NPTF is an American tapered pipe thread. BSPT and NPTF may look similar, but they have different thread angles and often different pitches. They should therefore not be combined without a suitable adapter.
What does JIC stand for?
JIC is a hydraulic coupling standard featuring UNF threads and a 37-degree sealing cone. When two sealing surfaces meet, the combined angle is 74 degrees, which explains the wording in the table.
The seal is formed against the cone, not inside the thread itself.
Do you need help identifying the right connection?
The choice of coupling is influenced by factors such as thread type, dimensions, sealing method, pressure, temperature, media, and how the connection will be installed. We’re happy to help you interpret a coupling designation and select a coupling that suits your application.
Contact us, and we'll help you find the right solution.
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