Measuring System: Nominal Pipe Size
Brass pipe fittings use a standard sizing system. This system is called Nominal Pipe Size (NPS). It refers to the approximate inside diameter of the pipe. The actual outside diameter is larger than the name. For example, a 1/2-inch fitting has an outside diameter of about 0.84 inches.
Small Fittings: 1/8 to 1/2 Inch
The smallest common brass pipe fittings start at 1/8 inch. These are used for instruments and controls. Next is 1/4 inch for small air and water lines. Then 3/8 inch for medium-duty applications. The 1/2-inch size is very common in homes. It serves sinks, toilets, and small appliances.
Standard Residential Sizes
Brass pipe fittings of 3/4 inch and 1 inch are standard. A 3/4-inch fitting handles main water lines. It also serves water heaters and washing machines. A 1-inch fitting is for larger supply lines. It distributes water to multiple fixtures. These sizes are typical in most houses.
Large Commercial Sizes
Larger brass pipe fittings go up to 4 inches. Sizes include 1-1/4, 1-1/2, and 2 inches. These are for commercial buildings and industrial use. A 2-inch fitting can be the main for a factory. A 4-inch size is for high-volume water or steam. These are heavy-duty components.
Metric Sizes for Global Markets
Many brass pipe fittings are also made in metric sizes. Common metric sizes are 8, 10, 12, 15, 18, and 22 mm. A 15 mm fitting is equivalent to 1/2 inch roughly. A 22 mm fitting is close to 3/4 inch. Metric fittings are standard in Europe and Asia. Always match metric to metric correctly.
Reducing Fittings for Size Transitions
A reducing fitting connects different pipe sizes. For example, a 3/4 x 1/2 fitting has two different ends. This allows a large pipe to feed a smaller line. Reducing couplings and bushings are common. They help adapt the system to fixture needs.
Compression Fittings: Sizes by Tube OD
Compression brass pipe fittings are different. They are sized by the tube’s outside diameter. Common tube ODs are 1/4, 3/8, 1/2, 5/8, and 3/4 inch. A 1/2-inch compression fitting fits a tube with 1/2-inch OD. This is not the same as pipe size. Tubing is measured by OD, not ID.
Flare Fittings: Sizes and Pressures
Flare fittings are used for gas and high pressure. They come in standard pipe sizes: 1/8 to 3/4 inch. A 3/8-inch flare fitting is common for gas lines. A 1/2-inch size is for larger appliances. Flare fittings can handle pressures from 600 to 3,000 PSI. This depends on the specific size.
Threaded Fittings: NPT vs. BSP
Brass pipe fittings use different thread standards. NPT (National Pipe Thread) is the US standard. BSP (British Standard Pipe) is used in many other countries. A 1/2-inch NPT has 14 threads per inch. A 1/2-inch BSP has a different thread pitch. These two are not interchangeable.
Elbow and Tee Sizes by Run and Branch
Elbows and tees have multiple size dimensions. A tee has a run and a branch. The run is the straight-through path. The branch is the side outlet. All three ends can be the same or different. For example, a 1/2 x 1/2 x 1/4 tee is common. This supplies a smaller branch line.
Nipple Lengths and Sizes
Pipe nipples are short threaded pipes. Standard brass pipe fittings include close, short, and long nipples. A close nipple has threads along its entire length. Lengths increase by 1/2-inch increments. Nipples are available from 1/8 to 2 inches in diameter. They connect two fittings together.
How to Identify the Correct Size
Always measure the fitting to confirm its size. Use a caliper for the most accuracy. The nominal size is stamped on most brass pipe fittings. For example, “1/2” means a 1/2-inch fitting. When in doubt, measure the thread diameter. Then compare it to a standard thread chart.
Brass pipe fittings are available in many sizes. Small fittings start at 1/8 inch for instruments. Residential sizes range from 1/2 to 1 inch. Commercial sizes go up to 4 inches and larger. Metric versions exist for global applications. Always verify the size and thread standard before buying. Matching sizes correctly ensures a leak-free connection.
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