Before you begin, please make sure to have the proper tools available. A seat angle gauge, thread pitch gauge, and an ID/OD caliper are necessary to make accurate measurements of commonly used connectors. Mid-State can provide these tools in one unit upon request.
The easiest way to identify thread types is by visually comparing your part with the pictures below, and then taking measurements of the thread ID/OD, threads per inch, and seat angles as appropriate. Compare measurements to the accompanying charts to identify the correct size.
Using an ID/OD caliper, measure the outside diameter of the male threads, or inside diameter of female threads and match results to the accompanying chart. Please note, results may vary if the caliper arms do not sit flush against the threads, or if the connection is worn from service.
If the port connection is angled, use a seal angle gauge to determine the proper seat angle. Female connections are usually measured by inserting the angle gauge into the connection and placing it on the sealing surface. If the connection and gauge are parallel, the correct angle has been determined. Male connections are usually measured by placing the gauge on the sealing surface. If the center-lines of the connection and gauge are parallel, the correct angle has been determined.
Use a thread pitch gauge to determine the number of threads per inch or the distance between threads in metric connections. Place the gauge on the threads until the fit is snug, and then match the measurements to the accompanying chart.
National Pipe Tapered Fuel (NPTF) is a connection widely used in fluid power systems, even though it is not recommended by the National Fluid Power Association for use in hydraulic applications. This thread is tapered and the seal takes place by deformation of the threads.
National Pipe Straight Mechanical (NPSM) is sometimes used in fluid power systems. The female half has a straight thread and an inverted 30° seat. The male is straight and has a 30° internal chamfer.
Measure thread diameter and subtract 1/4 inch to find the nominal pipe size.
SAE J514 37° JIC connection is very common in fluid power systems. Both the male and female halves of the connections have 37° seats. The seal takes place by establishing a line of contact between the male flare and the female cone seat. The threads hold the connection mechanically. Note – in sizes 02, 03, 04, 05, 08, and 10, the threads of SAE 37° and SAE 45° are the same, but the sealing surface angles are not.
SAE J514 Straight Thread O-Ring Boss connections are recommended by the N.F.P.A. for optimum leakage control in medium and high-pressure hydraulic systems. The male connector has a straight thread and an o-ring. The female port has a straight thread, a machined surface, and a chamfer designed to accept the o-ring. Sealing occurs when the o-ring is compressed into the chamfer. The threads hold the connection mechanically.
SAE J1453 O-Ring Face Seal connections offer the very best leakage control available. The male connector has a straight thread and an o-ring in the face. The female has straight threads and a machined, flat face. The seal occurs by compressing the o-ring init the flat face of the female. The threads hold the connection mechanically.
SAE J518 4-Bolt Flange is a connection widely used in fluid power systems. There are two pressure ratings. Code 61 is referred to as the standard series, while Code 62 is considered the 6000 psi series. The design concept for both series is the same, but the bolt hole spacing and flange head dimensions are larger for Code 62.
The female port is an threaded hole with four bolt holes in a rectangular pattern. The male consists of a flange head grooved for an o-ring, and either a captive flange or split flange halves with bolt holes to match the port. The seal occurs when the o-ring is compressed between the flange head and the flat surface surrounding the female port.
Caterpillar Flange connections share the same specifications and dimensions as Code 62 flanges, but with a flange head thickness of .56".
SAE J512 45° connections are commonly used in refrigeration, automotive, and truck systems. The connectors is frequently made of brass, but still available in steel. Both male and female connectors have 45° seats. The seal takes place between the male flare and female cone. The threads hold the connection mechanically.Note – in sizes 02, 03, 04, 05, 08, and 10, the threads of SAE 37° and SAE 45° are the same, but the sealing surface angles are not.
SAE J512 Inverted Flare connections are frequently used in automotive systems. The male connector can either be a 45° flare in the tube fitting form, or a 42° seat in the machined adapter form. The female has a straight thread with a 42° inverted flare. The seal takes place on the flared surfaces. The threads hold the connection mechanically.
British Standard Pipe Tapered (BSPT) connections are similar to National Pipe threads, except that the thread pitches are different in most sizes, and the thread form and outside diameters are close but not exactly the same. Because of the similarities to National Pipe, it is recommenced to very thread pitch and diameter closely with BSPT connectors. Sealing is accomplished by thread deformation.
British Standard Parallel (BSPP) connections are similar to National Pipe threads, except that the thread pitches are different in most sizes. The female swivel BSPP connector has a tapered nose/globeseal flareless swivel which seals on the cone seat of the male.
BSPP O-ring connections are also available in a "port" style which forgoes the chamfer in favor of a bonded seal which rests on the shoulder of the male and seals when compressed against the female. Some styles are available in "dual purpose" as well.
Japanese Industrial Standard, or JIS 30° Flare connections are similar to BSPP connections, and the threads of both fittings are interchangeable. JIS 30° fittings possess a cone that resembles JIC 37°, but have different flare angles and sealing principles.
While less commonly seen, JIS connectors are also available with a male inverted seat with metric threads, tapered pipe, and inverted male seat with parallel pipe threads. To identify these uncommon threads, please consult our downloadable guide or contact us for further assistance.
German DIN 7631 Series connections are often used in hydraulic systems. The male has a straight metric thread and a 60° recessed cone. The female has a straight thread and a tapered seat. The seal takes place by contact between the male cone and female nose/seat. The threads hold the connection mechanically.
German DIN 3902 Series connections consist of a common male and three different female types. DIN 3902 threads are also available in extra light (LL), light (L), and heavy duty (S) series. Selection of proper series is paramount to ensuring accurate identification.
The male has a straight metric thread, a 24° included angle, and a recessed counter bore that matches the tube OD used with it. The female may be a tube, nut and ferrule, a tapered flareless swivel, or a flareless swivel with o-ring, referred to as DKO type.