Brass Fitting Types and Sizes: A Complete Guide

Brass fittings are among the most widely used connection components in plumbing, hydraulic, pneumatic, and industrial fluid systems. Brass — an alloy of copper and zinc — delivers an exceptional combination of corrosion resistance, machinability, and mechanical strength that few other materials can match. Whether you are connecting water supply lines in a commercial building, assembling fuel delivery systems, or building out instrumentation tubing on a process skid, brass pipe fittings provide reliable, long-lasting joints that hold up under pressure and temperature cycling.

The versatility of brass fittings extends across nearly every industry. They resist dezincification in most water chemistries, tolerate moderate temperatures well above the range of many plastics, and offer natural antimicrobial properties that make them a preferred choice for potable water systems. With dozens of fitting styles available — from compression fittings and flare fittings to hose barb fittings and threaded NPT connections — selecting the right type and size for your application is critical. This guide walks through each major category of brass fittings, explains how to measure and size them correctly, and covers best practices for sealants, Teflon tape, and material compatibility.

Compression Fittings

Compression fittings create a seal by compressing a small brass or copper ring — called a ferrule or olive — against the outside diameter of the tubing as a threaded nut is tightened onto the fitting body. No soldering, brazing, or special tools are required, which makes brass compression fittings one of the most accessible and forgiving connection methods available. The ferrule deforms slightly as the nut draws it into the fitting body's tapered seat, forming a leak-tight mechanical seal around the tube.

These fittings are commonly used on copper, brass, aluminum, and some plastic tubing in water supply lines, refrigeration systems, and low-pressure instrumentation applications. Typical working pressures range from 150 to 300 PSI depending on the fitting size and tubing material. Because the connection is mechanical rather than permanent, compression fittings can be disassembled and reassembled — though reusing a ferrule that has already been compressed is not recommended for critical applications. Standard compression fitting sizes correspond to the outside diameter (OD) of the tubing, typically ranging from 1/8" to 1" OD. Browse our full selection of compression fittings.

Flare Fittings

Flare fittings use a machined 45-degree cone on the fitting body that mates against a flared end on the tubing itself. The tube end is flared outward using a flaring tool to create a precise 45-degree seat, and a flare nut draws the two surfaces tightly together. This metal-to-metal seal is robust and vibration-resistant, making flare fittings the standard choice in refrigeration, air conditioning, fuel gas systems, and automotive fuel lines. SAE J512 and SAE 45-degree flare standards govern the dimensions and tolerances for these connections.

Because the seal is formed between two precision-machined metal surfaces, flare fittings do not require thread sealant or Teflon tape on the flare joint itself. Proper flaring technique is essential — an uneven or cracked flare will leak regardless of how much torque is applied to the nut. Flare fittings are sized by the outside diameter of the tubing they accept, with common sizes running from 1/4" through 3/4" OD. They are particularly well suited for applications where the connection may be subjected to vibration or thermal cycling. Shop flare fittings at Apex Flow Solutions.

Inverted Flare Fittings

Inverted flare fittings look similar to standard flare fittings but reverse the sealing geometry. Instead of a male cone pressing into a female flare on the tube, the tube is flared inward and the fitting body features an internal cone seat. The inverted flare nut has a shorter thread engagement and a different seat angle than standard SAE flare nuts. This design originated in the automotive industry and remains the dominant connection method for steel brake lines, fuel lines, and transmission cooler lines in cars and trucks.

The inverted design provides a more compact connection profile and works exceptionally well with the double-flare technique used on soft steel tubing. Double flaring folds the tube end over on itself before seating, creating a stronger and more fatigue-resistant flare that withstands the high pressures and vibrations found in brake hydraulic systems. Inverted flare fittings use tube OD sizing — 3/16", 1/4", 5/16", and 3/8" are the most common sizes in automotive work. View our inverted flare fittings collection.

Flareless / Bite-Type Fittings

Flareless fittings — also known as bite-type or ferrule-type compression fittings — use a hardened ferrule that literally bites into the outside surface of the tubing when the nut is tightened. Unlike standard compression fittings where the ferrule simply compresses around the tube, the cutting edge of a bite-type ferrule digs a small groove into the tubing wall. This groove provides positive mechanical grip and a reliable seal, even under high pressures and vibration.

These fittings are widely used in hydraulic systems, instrumentation tubing, and process control applications where pressures may exceed 3,000 PSI. They work well with hard-drawn stainless steel, carbon steel, and copper tubing. Many designs use a two-ferrule system — a front ferrule that grips and seals against the tube, and a back ferrule that drives the front ferrule forward as the nut is tightened. Proper pre-setting (initial assembly with controlled torque) is important for consistent sealing performance. Explore flareless fittings for your instrumentation needs.

Hose Barb Fittings

Barb fittings feature a tapered, ridged stem — the barb — that is inserted directly into the bore of a flexible hose. The raised ridges on the barb grip the inside wall of the hose and resist pull-out forces. For low-pressure applications such as garden irrigation, aquarium plumbing, or coolant overflow lines, simply pushing the hose over the barb may provide an adequate connection. For any application involving meaningful pressure or hazardous fluids, a hose clamp — worm-gear style, crimp ring, or constant-tension spring clamp — is required to secure the hose against the barb.

Brass hose barb fittings are available in straight, elbow, and tee configurations, with barb sizes matching common hose inside diameters from 1/8" through 1" ID. The opposite end of the fitting typically features a male or female NPT thread for connection to a rigid pipe or port. When selecting barb fittings, match the barb size to the hose inside diameter — a slight interference fit (barb OD slightly larger than hose ID) ensures a secure grip. Shop brass hose barb fittings.

Push-to-Connect Fittings

Push-to-connect fittings offer the fastest installation of any brass fitting type. The tube is simply cut square, deburred, and pushed into the fitting body until it seats. Inside the fitting, a stainless steel grab ring locks onto the tubing while an O-ring provides the seal. No wrenches, solder, or special tools are needed. To disconnect, the release collar is pressed inward to disengage the grab ring, and the tube pulls free.

This style of fitting has become extremely popular in residential and commercial plumbing, particularly for PEX, copper, and CPVC tubing. They are equally useful in pneumatic systems and are rated for both hot and cold water supply. Push-to-connect fittings are available in sizes from 1/4" through 1" and in a full range of configurations including couplings, elbows, tees, and transition adapters. Because the O-ring provides the seal, no thread sealant is needed on the push connection itself. Find push-to-connect fittings for your project.

Pipe Fittings (NPT Threaded)

NPT (National Pipe Tapered) threaded brass pipe fittings are the backbone of rigid piping systems across industrial, commercial, and residential applications. The tapered thread design — with a 1-degree 47-minute taper per side — creates a progressively tighter fit as the fitting is threaded in, producing a wedging action that forms a seal along the thread flanks. NPT fittings include elbows, tees, couplings, bushings, nipples, caps, plugs, unions, and dozens of other configurations.

Because the NPT thread form is designed to seal on the threads themselves, thread sealant is required for a leak-free joint. Teflon tape, pipe thread sealant compound (pipe dope), or anaerobic thread sealant must be applied to the male threads before assembly. NPT pipe sizes are nominal — a 1/2" NPT fitting does not have a thread OD of 1/2 inch. Instead, NPT sizes correspond roughly to the inside diameter of the pipe they were historically designed to connect. Common brass pipe fitting sizes range from 1/8" NPT through 2" NPT. Browse brass NPT pipe fittings.

How to Measure Brass Fittings

Knowing how to measure brass fittings correctly prevents costly ordering mistakes and job-site delays. The measurement method depends on the fitting type. For compression fittings, the size refers to the outside diameter (OD) of the tubing the fitting accepts. Measure the tube OD with calipers — not a tape measure — for accuracy. A tube that measures 0.375" OD takes a 3/8" compression fitting. For hose barb fittings, the barb size corresponds to the hose inside diameter (ID), so measure the bore of the hose rather than its outside.

NPT pipe threads require a different approach because pipe sizes are nominal, not actual. The most reliable method is to measure the outside diameter of the male thread at its largest point using calipers, then cross-reference that measurement against an NPT thread chart. For example, a male thread measuring approximately 0.840" OD is a 1/2" NPT fitting. A thread pitch gauge helps confirm the threads-per-inch count — 14 TPI for 1/2" NPT, 18 TPI for 1/4" NPT, and so on. For flare fittings, measure the tubing OD that the flare nut slides over. If you are working with an unknown fitting, combining a caliper measurement with a thread gauge will identify both the size and thread standard in seconds.

Teflon Tape and Sealants: When to Use Them

One of the most common questions in fitting assembly is: do you use Teflon tape on brass fittings? The answer depends entirely on the fitting type. NPT tapered pipe threads require sealant — Teflon tape, pipe dope, or anaerobic sealant — because the threads themselves form the seal, and the small spiral gap between thread flanks needs to be filled to prevent leaks. Apply Teflon tape by wrapping the male threads clockwise (when viewed from the threaded end) with three to five wraps of tape, keeping the tape snug and within the thread area.

Compression fittings, flare fittings, and push-to-connect fittings should not have Teflon tape or sealant applied to their sealing surfaces. These fitting types achieve their seal through mechanical means — a compressed ferrule, a metal-to-metal flare seat, or an O-ring — and adding tape or dope to those sealing surfaces can actually prevent proper contact and cause leaks. If an NPT thread is present on one end of a compression or barb fitting, sealant is appropriate on that NPT connection only. Pipe dope (thread sealant compound) is an alternative to Teflon tape that some technicians prefer because it lubricates the threads during assembly and fills irregularities more effectively on larger pipe sizes.

Material Compatibility: Brass Fittings for Gas, Water, and More

Can you use brass fittings for gas? Yes — brass is widely approved for natural gas and propane systems, and many gas codes specifically call for brass or steel fittings on fuel gas piping. Flare fittings are the most common connection method in gas distribution because their metal-to-metal seal is inherently resistant to gas permeation. When using brass in gas service, verify that the fittings meet CSA or UL listings for fuel gas, and always follow local codes and the Authority Having Jurisdiction (AHJ) requirements.

For potable water applications, lead-free brass is required by the Safe Drinking Water Act and NSF/ANSI 61 standards. Lead-free brass fittings contain no more than 0.25% lead by weighted average across wetted surfaces. Standard (leaded) brass, which may contain 1–4% lead for improved machinability, remains acceptable for non-potable industrial services, compressed air, oil, and many chemical applications. Brass performs well with most petroleum-based fluids, glycol mixtures, and mild chemical solutions. However, brass should be avoided in contact with ammonia, acetylene, and certain acidic or high-chloride environments that can cause stress corrosion cracking or dezincification. When in doubt, consult a chemical compatibility chart or contact our technical team.

Common Brass Fitting Sizes: Quick Reference

Brass fittings are manufactured in a standard range of sizes across all fitting types. Compression fittings are available in tubing OD sizes of 1/8", 3/16", 1/4", 5/16", 3/8", 1/2", 5/8", 3/4", and 1". NPT pipe fittings are stocked in nominal pipe sizes of 1/8", 1/4", 3/8", 1/2", 3/4", 1", 1-1/4", 1-1/2", and 2". Flare fittings follow tubing OD sizing at 1/4", 3/8", 1/2", 5/8", and 3/4". Hose barb sizes match hose ID in increments of 1/8" from 1/8" through 1". Many brass fittings are also available in metric sizes — 4mm, 6mm, 8mm, 10mm, 12mm, and 16mm are the most common — for use with metric tubing and equipment. Adapter fittings that transition between NPT threads and compression, flare, or barb connections are available in nearly every size combination.

Find the Right Brass Fittings for Your Application

Selecting the correct fitting type, size, and material grade is essential for safe, leak-free system performance. Whether you need brass compression fittings for a water line, flare fittings for a gas installation, or NPT pipe fittings for an industrial process, Apex Flow Solutions stocks a comprehensive inventory of brass fittings ready to ship. Visit our Brass Fittings Hub to browse by fitting type, or contact our team for sizing assistance and technical support on your next project.