The Tools You'll Need

You can't do this job right by eye-balling it. To stop guessing, you need two basic tools that should be in every shop:

• Calipers: A simple set of digital or dial calipers is non-negotiable for getting an accurate measurement of the thread diameter.
• Thread Pitch Gauge: This little set of "leaves" with teeth is the only reliable way to measure thread pitch. They're cheap, and they save you a ton of headaches. Get one with both imperial (TPI) and metric blades.

The 4-Step Process for Hydraulic Fitting Identification

Every hydraulic fitting in the world can be identified if you follow this simple process. Don't overthink it.

Step 1: Tapered or Straight? (The Eye Test)

This is the first and most important cut. Look at the male threads. Do they form a cone, getting smaller at the end? Or are the threads parallel, like a bolt? This tells you almost everything you need to know about the hydraulic thread types.

• If TAPERED: You have a pipe thread (like NPT or BSPT). The seal is made on the threads themselves, and it needs sealant.
• If STRAIGHT (PARALLEL): You have a modern fitting (like JIC, ORB, ORFS, BSPP, or Metric). The threads just provide clamping force. The seal is made somewhere else.

Step 2: Measure the Thread Diameter (The Caliper Test)

Now, how to measure hydraulic fittings: use your calipers to get the outside diameter (OD) of the male threads. For female threads, measure the inside diameter (ID). Write this number down. This is the first step in creating your own hydraulic fitting size chart for the job at hand.

Heads Up on Pipe Threads: The nominal size (like "1/2-inch NPT") is not the actual measurement. You MUST use a reference chart to convert your measured diameter to the correct pipe size.

Step 3: Determine the Pitch (The Gauge Test)

Your thread pitch gauge will tell you how coarse or fine the threads are. This is how you tell the difference between an NPT and a JIC of the same diameter. Find the leaf that sits perfectly in the threads.

• For American threads (NPT, JIC, ORB, ORFS), you're measuring Threads Per Inch (TPI).
• For Metric and British (BSP) threads, you're measuring the pitch in millimeters.

Step 4: Identify the Sealing Method (The Visual Clues)

This is the final piece of the puzzle, especially for straight threads. The design of the fitting itself is your hydraulic fitting identification chart:

• A 37-degree metal cone on the end? That's a JIC (SAE J514) fitting.
• An O-ring at the base of the threads? That's an SAE O-Ring Boss (ORB).
• A flat face with a groove for an O-ring? That's an O-Ring Face Seal (ORFS).
• A tapered thread with a 55-degree angle (check your gauge)? You're looking at a BSPT (British Standard Pipe Taper).
• A straight thread that takes a bonded seal washer? It's likely a BSPP (British Standard Pipe Parallel).

With these four data points—Taper, Diameter, Pitch, and Seal Type—you can use any official hydraulic fitting chart to confirm the exact standard and size.

Common Mistakes That Lead to Leaks

• Mixing NPT vs. BSP Threads: They look similar but have different thread angles. They will cross-thread, damage the port, and leak. Don't do it.
• Confusing Dash Size with Thread Size: The dash size tells you the TUBE size, not the thread size. A -8 (1/2") tube can have many different thread sizes depending on the fitting type (JIC, ORFS, etc.). Always measure the thread itself.

The Bottom Line

Learning how to size hydraulic fittings isn't magic. It’s a simple process. Take a minute to measure correctly, and you’ll stop wasting hours with returns and clean-ups. Using the right tools and this guide, you can confidently identify any fitting on your bench.