JIC, BSP and metric fittings compared — a hydraulic connection selection guide
The three common hydraulic crimped connection standards, how their threads and sealing angles differ, and which to specify on which project.
Why does the connection type matter?
One of the most common errors when assembling hydraulic lines is joining two parts made to different thread standards or sealing angles. Even when two fittings look alike and the threads can be forced together, a mismatch in the sealing face angle causes leakage under pressure or damages the thread. The three standards below are the most widely used hydraulic crimped connections in the oil, gas and petrochemical industries and on industrial machinery.
A technical comparison of the three standards
| Property | JIC 37° | BSP | Metric 24-degree |
|---|---|---|---|
| Reference standard | SAE J514 / ISO 8434-2 | BS 5200 | ISO 8434-1 / DIN 3861 |
| Sealing angle | 37-degree flare (metal-to-metal) | Usually an elastomeric washer or O-ring on a flat face | 24-degree cone (metal-to-metal or with an O-ring) |
| Thread form | UN/UNF (inch, unified) | BSPP (parallel) or BSPT (tapered), inch based | Metric (millimetre based) |
| Origin / regional prevalence | North America; the dominant standard in the global hydraulics industry | The UK and Commonwealth countries; common on European and Asian equipment of British origin | Europe (particularly Germany); common on equipment of European origin |
Why mixing these three standards is dangerous
Because all three types look alike — a tapered or straight thread with a nut on the hose — they can easily be substituted for one another by mistake in the store or on site. An incorrect pairing, such as running a BSP nipple into a JIC nut, may appear to tighten at first, but at working pressure the mismatched sealing angle causes a leak or even strips the thread. Identifying the exact connection type from the drawing or the OEM equipment specification before ordering is therefore essential.
Selection criteria for the buyer
- Matching existing equipment: The most important criterion is matching the connection standard of the pump, valve or cylinder already installed. That detail is usually given in the catalogue or on the nameplate of the original equipment.
- Origin of the project equipment: Machinery of American origin usually uses JIC; equipment of British or Commonwealth origin usually uses BSP; and German or wider European equipment usually uses metric.
- Ease of maintenance: On new projects with no existing equipment to match, JIC is usually the simpler choice, because spare parts are widely available on the global market.
- If in doubt: Measure the thread diameter and pitch accurately with a thread gauge, or send us a sample or a photograph with a ruler alongside, so the connection type can be identified precisely. Guessing from appearance is high risk.
Not sure which connection standard you need?
Send us a photograph or a sample of your existing fitting and we will identify its exact standard and propose the equivalent connection.