Understanding the various thread types and sealing methods for hydraulic fittings is crucial. While there are numerous hydraulic fittings and connectors, standards exist for connecting these components to pipes. 

BSP and NPT Thread Styles

The two most common thread styles globally are Automotive Lift Repair Florida British Standard Pipe (BSP) and National Pipe Taper (NPT). They serve as the international standards for connecting fittings and pipes. However, it’s important to recognize the differences between these thread styles.

BSP Threads

Automotive Lift Repair Florida BSP threads are based on ISO 228 and the Whitworth standard. The BSP standard, which includes Whitworth threads developed in 1841, is widely adopted internationally for interconnecting and sealing pipes and fittings. Whitworth was the world’s first screw thread standard and remains popular for pipe and fitting connections.

NPT Threads

NPT threads are used alongside National Pipe Straight Mechanical (NPSM) parallel threads in the U.S. They are the U.S. standard for pipe connections, but NPT and BSP threads are not interchangeable due to their differing thread forms. NPT threads are pointed, while BSP threads are rounded. Additionally, NPT threads have a 60-degree angle, whereas BSP threads have a 55-degree angle. Attempting to connect NPT male threads with BSPP female threads can result in misalignment, causing fluid leakage or even catastrophic failure under pressure.

BSPP Parallel and BSPT Tapered Threads

BSP threads, derived from British Standard Whitworth (BSW), include both parallel and tapered types. BSW threads, created by Joseph Whitworth in 1841, were the first national screw thread standard and led to the widespread use of BSP.

– Automotive Lift Repair Florida BSP Parallel Threads: Also known as “G” threads, these are commonly used with O-rings or retaining rings to ensure a secure seal. They are prevalent in markets such as the UK, Europe, Asia, Australia, New Zealand, and South Africa due to their excellent sealing properties and ease of installation. BSPP pressure gauges use copper crush washers for a pressure-tight seal, eliminating the need for thread sealants.

– BSPT Tapered Threads: These fittings typically seal through metal-to-metal wedging but can also be used with O-rings or bonded washers. BSPT fittings are designed for use in machined surfaces, providing a reliable seal when assembled with lubricants or sealants.

BSP Adaptor Pressure Ratings

The following chart provides design working pressures for BSP adaptors. These pressures are guidelines and are not definitive specifications.

Working pressure represents the ideal maximum pressure for the application, proof pressure is the highest pressure that can be applied without affecting performance, and over pressure is the pressure at which the device is likely to burst.

BSP fittings come in a variety of materials, including steel, stainless steel, alloys, and brass, and are used in diverse applications ranging from oil and gas to industrial machinery.

Thrust-Wire Fittings

Automotive Lift Repair Florida Thrust-wire fittings feature small, rigid wires inserted into holes in a nut or fitting, enhancing the connection’s durability. These fittings, available in BSP (with a proof pressure of 8,000 PSI) or JIC (with a proof pressure of 6,000 PSI) styles, are designed for high-pressure and high-vibration environments. They are among the most robust and reliable fittings available.

Though not as widely used as other fittings due to their more complex installation, thrust-wire fittings are essential in applications with significant vibration. They are typically made from high-grade carbon or stainless steel, depending on the pressure and type of fluid or gas. These fittings are often locally induction hardened to withstand high torque and internal wear.

Despite their strength, thrust wires can be ejected from the assembly, leading to potential catastrophic failure. To prevent this, the hole should be deformed after inserting the thrust wire to secure it against vibration.

Thrust-wire fittings are commonly used in construction, agriculture, oil and gas, and mining equipment due to their durability under repeated vibration. They are also effective in industrial settings where hoses are frequently actuated, especially under high pressure.

Automotive Lift Repair Florida Banjo Fittings

Banjo fittings are used primarily in low-pressure pneumatic systems. They consist of a hollow bolt and a spherical union for fluid transfer, and their design resembles a banjo, with a large circular section connected to a thinner pipe. Typically made from carbon steel, banjo fittings can also be crafted from other materials depending on the application.

Unlike standard pipe fittings, banjo fittings do not require rotation relative to the host fitting. This feature reduces the risk of damaging the hose by twisting during installation and allows for the adjustment of the pipe’s exit direction independently from the fitting.

Common applications for banjo fittings include:

– Brake caliper connectors

– Carburetor connectors

– Hydraulic clutch systems

– Hydraulic power systems

– Power steering fluid connections

– Turbocharger oil feeds

– Variable valve timing systems

Recently, they are also used in fuel dosing systems for Selective Catalytic Reduction (SCR), a technology that significantly reduces nitrogen oxides in diesel engine exhaust.

Automotive Lift Repair Florida AN Fittings

The Army Navy (AN) standard is a design specification for U.S. military aviation applications, known for its strict performance requirements. Originally used by military OEMs and contractors, AN fittings are now also found in civilian applications but are often confused with the Society of Automotive Engineers (SAE) 37-degree fittings. By the mid-20th century, 37-degree flare fittings became common in industrial markets, leading to confusion with AN standards.

Automotive Lift Repair Florida JIC Fittings

To address the confusion surrounding AN fittings and to standardize manufacturing practices, the Joint Industrial Council (JIC) established specification standards, notably the JIC 37-degree fitting. Although JIC fittings have slightly lower thread quality compared to AN fittings, they are more cost-effective and suitable for general applications. SAE has since adopted the JIC standard.

Today, JIC fittings adhere to SAE J514 and MIL-DTL-18866 standards and are commonly made from various materials, including forged carbon steel, stainless steel, brass, Monel, and nickel-copper alloys. They are used in high-pressure applications up to 5,000 PSI for smaller bore diameters.

While JIC (or SAE) 37-degree fittings are generally interchangeable with AN fittings, they are not suitable for military aviation or aerospace applications. Instead, they are used in industrial, construction, agricultural, and heavy machinery contexts.