JIC Fittings Guide › JIC vs NPT

JIC vs NPT: 37° Flare vs Tapered Pipe Thread Fittings

JIC and NPT are two of the most common connections in North American hydraulic and fluid systems, and they often appear on the same machine: an NPT port on a pump or valve body, and JIC hose ends running between components. They look superficially similar because both are threaded, but they seal in completely different ways. This guide explains the difference, shows how to identify each, and covers when to use JIC-to-NPT adapters. For the full JIC size chart, see the main JIC fittings guide.

The Short Answer

A JIC fitting (SAE J514 / ISO 8434-2) seals metal-to-metal on a 37° flared cone. Its threads are straight (parallel) UNF/UN threads that only clamp the two halves together. An NPT fitting (ASME B1.20.1) seals on the threads themselves: the threads are tapered at 1°47′ to the centerline, so the male wedges into the female as it is tightened. Because the crests and roots of NPT threads do not fully close up, Swagelok and ASME both state that a sealant is required for a pressure-tight NPT joint. JIC needs no sealant at all.

How Each Fitting Seals

JIC: a flare seal

Both halves of a JIC connection have a 37° seat. The male has a 37° cone nose; the female swivel nut carries a matching 37° seat or clamps a flared tube. Tightening the nut draws the two cones together and creates a line of metal-to-metal contact. The threads carry the mechanical load but play no part in sealing. That has practical consequences:

• No PTFE tape or pipe dope. Sealant on JIC threads does nothing for the seal and can shed into the hydraulic fluid.
• The joint can be disconnected and reconnected repeatedly, provided the flare is not damaged.
• The swivel nut lets you orient a hose or elbow without rotating the whole fitting body.
• A scratched or cracked flare will leak no matter how hard the nut is tightened.

NPT: a thread interference seal

NPT threads have a 60° thread angle and flat-truncated crests and roots. As the male tapers into the female, the flanks interfere and deform. ASME B1.20.1 says NPT joints are intended to be made up wrench-tight with a sealant whenever a pressure-tight joint is required, and Swagelok notes that a good sealant also acts as an anti-galling lubricant. Consequences:

• Sealant (PTFE tape, paste, or anaerobic sealant) is always needed.
• Orientation is set by how far the fitting is tightened, so aligning an elbow means over- or under-tightening.
• Every reassembly deforms the threads further, so repeat make-up and break-out degrades the joint.
• Over-tightening can crack a female port casting.

How to Tell JIC and NPT Apart

1. Look at the end. A male JIC has a smooth 37° cone past the last thread. A male NPT has threads right to the end, with no sealing cone.
2. Check for taper. Measure the thread OD at the first and last full threads. NPT gets noticeably smaller toward the end; JIC stays the same diameter.
3. Count threads per inch. Common NPT pitches are 27 TPI (1/8"), 18 TPI (1/4" and 3/8"), 14 TPI (1/2" and 3/4") and 11.5 TPI (1" to 2"). JIC uses 24, 20, 18, 16, 14 and 12 TPI. 18 and 14 appear in both, so pitch alone is not conclusive.
4. Measure the OD. NPT sizes are nominal pipe sizes, so a 1/4" NPT male actually measures about 0.54" and a 1/2" NPT about 0.84". A JIC thread measures close to its nominal size (a 3/4-16 JIC measures about 0.75").

Our step-by-step JIC identification guide walks through the full process with calipers, a pitch gauge and a seat angle gauge.

Side-by-Side Comparison

Common JIC-to-NPT Size Pairings

Adapters are usually sold by matching dash sizes on each end. The table below shows the pairings commonly stocked by hydraulic distributors. NPT thread pitches are per ASME B1.20.1; JIC threads per SAE J514.

Mixed-size adapters (for example -6 JIC male × 1/2" NPT male) are also widely available, so always specify both ends.

When to Use Each

Choose JIC when

• The connection will be broken and remade during maintenance.
• You need to orient an elbow or tee precisely.
• You want to keep sealant out of the hydraulic system.
• You are connecting hose ends or flared tube between components.

NPT is common when

• The equipment port is already NPT — older pumps, valves, gauges and cylinders often are.
• The connection is low-cycle and rarely disturbed, such as a plug or gauge port.
• You are working with general pipe systems rather than hydraulic tube or hose.

Many hydraulic designers prefer straight-thread ports (such as SAE O-ring boss) over NPT for new designs because they seal with an O-ring rather than thread interference, but NPT remains widespread in the installed base.

Using JIC-to-NPT Adapters Correctly

1. Install the NPT end first. Apply sealant to the male NPT threads only, leaving the first thread or two bare so sealant does not enter the system. Tighten wrench-tight; ASME B1.20.1 gives no standard torque or turn count.
2. Keep sealant off the JIC end. The flare must be clean and dry of tape or paste.
3. Tighten the JIC nut to the manufacturer's torque or flats-from-wrench-resistance value. Over-tightening a flare can deform the cone.
4. Specify material. Zinc-plated carbon steel is standard; 316 stainless is used for corrosive or washdown environments.

Getting the Order Right

Most ordering mistakes come from mixing up nominal sizes. A "1/2-inch" NPT is about 0.84" across the threads, while a -8 JIC (for 1/2" tube) has a 3/4-16 thread. When you request a quote, list each end separately — e.g. "-8 JIC male × 1/2" NPT male, straight, zinc-plated steel, qty 50". For more comparisons see JIC vs ORFS and JIC vs AN, and our JIC thread size chart.

FAQ

Related guides

• JIC Fittings Guide (main)
• JIC vs ORFS
• JIC vs AN
• How to Identify a JIC Fitting
• JIC Thread Size Chart
• -4 JIC Fittings
• -6 JIC Fittings
• -8 JIC Fittings
• -10 JIC Fittings
• -12 JIC Fittings
• -16 JIC Fittings
• JIC vs SAE 45° Flare
• JIC vs BSPP
• JIC vs Metric (DIN 24°)
• JIC Torque Specs
• JIC Fitting Types
• JIC Materials & Pressure Ratings

Request a Quote