Thread chart: AN fittings guide

If you are unsure which AN fitting, adapter or nipple you need, you can find a practical thread chart here with sizes and dimensions for many different thread types. The chart makes it easier to compare dimensions and find the right solution, whether you are working with a fuel system, oil system, cooling system or other custom-built automotive installations.

AN fittings are often used within motorsport, tuning and special projects, where higher demands are placed on sealing, durability and flexibility. They are popular for fuel systems, oil coolers, transmission coolers, aluminium radiators, as well as oil feed and return lines. When working with AN systems, it is important to choose the correct thread type and size so your fittings and adapters match properly.

At Qualitec, we offer a wide range of AN fittings, adapters and nipples in many sizes and colours, including black, blue and red. They can also be specially ordered in all colours and optionally with the customer’s logo for larger orders.

Whether you need a straight fitting, an angled fitting, a reducer or a specific adapter, it is important to choose the right type from the beginning so you avoid wrong orders and unnecessary problems during installation. See our large selection of AN fittings!

Identify Hydraulic Threads: The Workshop Guide

Using the wrong thread costs time, seals, and components.
This guide gives you a quick, reliable, and hands-on method to identify fittings in the field — without flipping through thick standards.

What to Look For (Before Pitch and Size)

A. How does the connection seal?

• In the thread itself: Tapered pipe threads (e.g. NPT/NPTF, BSPT).

• Against a flat face: Parallel threads with a flat front face + O-ring or bonded washer (e.g. ORFS, BSPP with bonded seal).

• Metal-to-metal: Flare connection (e.g. JIC 37°, DIN 24°).

B. What does the geometry and hardware reveal?

• O-ring in the face → parallel male (ORFS, BSPP port, ISO 6149 port).

• Tube nut and ferrule/cutting ring → JIC 37° or DIN 24°.

• Visible taper → tapered pipe thread.

10-Minute Workflow (Step-by-Step)

1. Taper Test (30 sec)
Gently hold the caliper jaws around the male thread and slide along 5–7 threads.
If it gets noticeably tighter or looser, it’s tapered.

2. Face/Port Check (30 sec)
Flat, polished face? Look for an O-ring (ORFS) or a flat sealing surface for a washer (BSPP/ISO ports).
Flare seat/cone? Check the angle (see step 5).

3. Pitch (2 min)

• Metric: Measure the distance between two adjacent crests in mm using a pitch gauge.

• Inch (UN/BSP/NPT): Use a pitch gauge with threads per inch (TPI).

Tip: Hold the gauge against a bright background; try neighboring blades if one “almost fits.”

4. Size (3 min)

• Pipe threads (BSP/NPT): Think nominal size – measure OD (outside diameter) with a caliper and match to the nearest pipe size (measured OD is usually larger than the nominal).

• Non-pipe (UN/UNF/metric): Use measured OD + pitch → that’s your size.

5. Seat Angle (2–3 min)

• JIC 37° vs. SAE 45°: Use an angle/flare gauge on the seat; 37° is flatter than 45°.

• DIN 24°: Noticeably shallower angle; typically used with a cutting ring (DIN 2353 / ISO 8434-1).

6. Notation (1 min)
Always write [size] – [type] – [pitch] – [seat/sealing].
Examples:

• M14×1.5 – ISO 6149 port

• 3/4-16 UNF – JIC 37°

• G1/4 – BSPP with bonded seal

• R1/2 – BSPT

• 1/4-18 NPT

Quick ID: How to Tell the “Lookalikes” Apart

Metric Parallel vs. BSPP (G)

• Pitch: Metric in mm (e.g. 1.5) vs. TPI (e.g. 19).

• Notation: M…×… vs. G….

• In practice: Both appear in EU/DK equipment – measure pitch first, then check port/seal type.

JIC 37° vs. SAE 45° Flare

• Angle: 37° is flatter; 45° is steeper.

• Result: They screw together – but leak under pressure. Do not mix.

BSPP (parallel) vs. BSPT (tapered)

• Taper test: Reveals the difference in seconds.

• Sealing: BSPP seals on a flat face with O-ring/bonded seal; BSPT seals in the threads.

ORFS vs. “Flat Face” Without O-ring

• ORFS: Distinct O-ring in the male face; parallel UNF threads.

• Flat face without O-ring: Expect a bonded washer in the port (BSPP/ISO).

Field Tests & Memory Tricks

• 10-Tooth Trick (metric): Measure over 10 thread peaks and divide by 10 → pitch in mm (compensates for wear/dirt).

• Marker Test for Taper: Draw a thin line of marker along the thread. Screw into a known parallel nut 1–2 turns – if the ink rubs only at tip or root, it’s tapered.

• OD minus 1/4” (rule of thumb): For pipes up to ~2", OD − 1/4" ≈ nominal pipe size (verify with pitch).

• “O-ring = parallel” is often true for male ends.

Common Hydraulic Threads (Overview)

(Table is indicative – always confirm with measurements.)

Troubleshooting (Quick Overview)

Ordering Examples

• G3/8 – BSPP – 19 TPI – bonded seal

• R1/2 – BSPT – 14 TPI – tapered

• 1/4-18 NPT – tapered – with thread sealant

• 3/4-16 UNF – JIC 37° – male

• M18×1.5 – ISO 6149 port – O-ring

Tool List (Small Kit, Big Value)

• Caliper (0.01 mm)

• Thread pitch gauge (mm + TPI)

• Angle/flare gauge (37° / 45° / 24°)

• Reference chart for nominal pipe sizes

• Marker + flashlight

Abbreviations for the different thread types:

A.P.I. = American Petroleum Institute Taper Thread
A.S.A.E. = American Society of Agricultural Engineers
A.S.S.P.T. = American National Straight Pipe Thread
B.S.P. = British Standard Parallel Pipe Thread
B.S.P.T. = British Standard Pipe Tapered Thread
D.I.N. = Deutsches Institut für Normung
F.I.E.I. = Farm Industrial Equipment Institute
F.P.T. = Female Pipe Thread
G.H.T. = Garden Hose Threads
I.P.T. = American Iron Pipe Thread - Straight
J.I.C. = Joint Industri Conference (SAE37)
J.I.S. = Japaneese Industrial Standard
M. = Metric Thread
M.M. = Metric Thread
N.P.S. = American National Pipe Thread - Straight
N.P.S.M. = American National Pipe Thread - Straight Mecanical
N.P.T. = American National Pipe Thread - Taper
N.P.T.F. = American National Pipe Thread - Taper (Dry seal)
N.S.T. = American National Standard Thread - Straight
R. = Rørgjenger (BSP)
R.T. = British Round Thread
S.A.E. = Society of Automative Engineers
U.R.T. = Dennis Urban Round Thread
U.N.C. = Unified Coarse Thread
U.N.F. = Unified Fine Thread
U.N.S. = Unified National Special
V.E.E. = Shelvoke Drewry “VEE“ Round Thread
W. = Withworth Thread