S'expliquen les mides dels accessoris de canonada de llautó: Fils, Dimensions i Guia de selecció

Escollir l'ajust de llautó adequat no és tan senzill com fer coincidir dos números. Un encaix marcat 1/2 polzada does not necessarily have a 1/2-inch thread diameter, and a fitting with a similar measured diameter may still use a completely different thread standard.

Comprensió brass pipe fittings sizes, thread dimensions, nominal pipe size, and thread standards is essential when selecting brass elbows, samarretes, acoblaments, adaptadors, connectors de mànega, and other threaded fittings.

This guide explains the most common brass fitting sizes, Rosca NPT i BSP, how to measure a brass fitting, and how to specify the correct size when ordering.

Acoblament de canonada de llautó

What Does “Acoblament de canonada de llautó Size” Actually Mean?

When suppliers or buyers refer to a brass fitting size, they are usually referring to the nominal connection size, not the actual physical diameter of the fitting.

Several different measurements may be involved:

Measurement	What It Means
Mida nominal	Standardized size designation, such as 1/2″ or 1″
Tub OD	Actual outside diameter of the pipe
Thread Major Diameter	Largest diameter across an external thread
Thread Minor Diameter	Smallest diameter of the thread profile
Thread Pitch	Distance between adjacent threads
TPI	Fils per polzada
Fitting Body OD	Outside diameter of the fitting body

Per exemple, a 1/2″ NPT brass fitting has a nominal size of 1/2 polzada, but its external thread major diameter is approximately 0.840 polzada (21.34 mm).

This is why simply measuring a fitting with a caliper is not enough to identify its size.

Nominal Size vs. Actual Diameter

The nominal size is a standardized designation used to describe the pipe or connection. It should not automatically be interpreted as the actual thread diameter or pipe outside diameter.

For accurate identification, check the following together:

• Nominal fitting size
• Fil estàndard
• Rosca mascle o femella
• Thread major or internal diameter
• TPI or thread pitch
• Thread profile

Important: The dimensions in the following tables are standard reference dimensions for thread identification. Actual product dimensions can vary according to the applicable standard, tolerance, disseny d'ajust, and manufacturer.

Nominal Size vs. Actual Diameter

Acoblament de canonada de llautó Size Chart

The most common brass pipe fittings are available in sizes ranging from small plumbing connections to larger industrial piping systems.

The following table provides common reference sizes for BSP threads:

Mida nominal	BSP Thread Major Diameter	TPI
1/8″	9.728 mm	28
1/4″	13.157 mm	19
3/8″	16.662 mm	19
1/2″	20.955 mm	14
3/4″	26.441 mm	14
1″	33.249 mm	11
1-1/4″	41.910 mm	11
1-1/2″	47.803 mm	11
2″	59.614 mm	11

These dimensions refer to the fil, not the overall outside diameter of the brass fitting.

Per exemple, a 1/2″ BSP threaded fitting has a thread major diameter of about 20.955 mm. The body of the elbow, samarreta, or coupling will normally be larger.

Common Brass Fitting Sizes

For plumbing, HVAC, aigua, gas, and general industrial applications, commonly requested brass fitting sizes include:

• 1/8″
• 1/4″
• 3/8″
• 1/2″
• 3/4″
• 1″
• 1-1/4″
• 1-1/2″
• 2″

Smaller sizes are common in instrumentation, small water lines, and hose connections, while larger sizes are frequently used in industrial and commercial piping.

1/2″ Encaix de llautó

NPT Brass Fitting Sizes

NPT (National Pipe Taper) is one of the most widely used inch-based pipe thread standards, particularly in North America.

NPT threads are tapered and use a 60-degree thread form. The thread dimensions are standardized under ASME B1.20.1.

A typical NPT brass fitting size chart is:

Nominal NPT Size	Aprox. External Thread Diameter	TPI
1/8″	0.405″ (10.29 mm)	27
1/4″	0.540″ (13.72 mm)	18
3/8″	0.675″ (17.15 mm)	18
1/2″	0.840″ (21.34 mm)	14
3/4″	1.050″ (26.67 mm)	14
1″	1.315″ (33.40 mm)	11.5
1-1/4″	1.660″ (42.16 mm)	11.5
1-1/2″	1.900″ (48.26 mm)	11.5
2″	2.375″ (60.33 mm)	11.5

Aquests són thread reference dimensions, not the overall dimensions of the fitting.

Per exemple, if you measure approximately 21.3 mm across the external thread of a fitting, it may be a 1/2″ NPT thread. No obstant això, diameter alone does not prove that identification. TPI and thread profile should also be checked.

Why NPT Size Can Be Confusing

A common mistake is assuming:

1/2″ NPT = 1/2″ thread diameter

It does not.

La 1/2″ designation refers to the nominal pipe size, while the external thread diameter is approximately 0.840 polzada.

This difference is normal for pipe thread sizing and is one of the main reasons buyers should specify the complete thread standard when ordering brass fittings.

NPT Brass Fitting Sizes

BSP Brass Fitting Sizes

BSPP (Paral·lel) i BSPT (Cònic)

BSP—British Standard Pipe—is the dominant thread family in the UK, Europa, and many Commonwealth markets. Unlike NPT, BSP comes in two distinct forms:

BSPP (G thread, ISO 228-1): Parallel threads. They do not seal on the threads themselves. A separate sealing surface—usually a bonded washer, O-ring, or gasket—provides the seal.

BSPT (R/Rp thread, ISO 7-1): Tapered threads. Like NPT, BSPT seals by thread compression. No obstant això, the thread angle is 55 graus (Whitworth form), not 60 graus.

Common BSP Sizes

BSP Size	Aprox. Major OD	TPI
1/8″	9.728 mm	28
1/4″	13.157 mm	19
3/8″	16.662 mm	19
1/2″	20.955 mm	14
3/4″	26.441 mm	14
1″	33.249 mm	11
1-1/4″	41.910 mm	11
1-1/2″	47.803 mm	11
2″	59.614 mm	11

Thread dimensions per ISO 228-1 (BSPP) i ISO 7-1 (BSPT). Angle del fil: 55° (Whitworth form). BSPP is parallel; BSPT is tapered at 1:16.

A common field observation: A thread measuring roughly 1/2 polzada (12.7 mm) across the outside is likely a1/4″ BSP thread, not a 1/2″ BSP. La 1/2″ BSP thread actually measures20.955 mm across its major diameter. This “quarter-inch larger” rule of thumb holds approximately for BSP sizes up to about 1″, but always verify with a thread gauge rather than relying on visual estimation alone.

BSP Brass Fitting Sizes

NPT vs BSP: Why the Same Size May Not Fit

This is not a deep comparison—there is a dedicated article coming on that topic. But you need to know the essentials:

Característica	NPT	BSP
Mercat primari	Amèrica del Nord	Regne Unit, Europa, Commonwealth
Angle del fil	60°	55°
Common Types	NPT (afilat)	BSPP (paral·lel), BSPT (afilat)
Seal Method	Thread compression + sealant	BSPP: gasket/washer; BSPT: thread compression
Intercanviable?	No	No

Never specify a brass fitting only as “1/2 inch.” Always confirm the thread standard.

Even when nominal sizes match—for example, both are labeled 1/2″—NPT (60° angle del fil) i BSP (55° Whitworth) will not thread together properly. The 5° angle difference causes cross-threading and guarantees leaks. Forcing them together damages both threads.

How to Measure a Brass Pipe Fitting

When you have an unmarked fitting in hand, five measurements will identify it:

Pas 1: Check the Fitting Type

Colze, samarreta, acoblament, adaptador, or connector? The type tells you what the fitting does, but not its size.

Pas 2: Measure the Thread Diameter

Use a vernier caliper. For male threads, measure across the outside diameter at the widest point. For female threads, measure the inside diameter.

Pas 3: Count the Threads (TPI)

Use a thread pitch gauge or place a ruler along the thread and count how many complete threads fit within one inch. This is the TPI.

Pas 4: Identify the Thread Profile

Tapered or parallel? NPT and BSPT taper; BSPP and metric threads are parallel. Roll the fitting on a flat surface—a tapered thread will wobble visibly.

Pas 5: Check Male or Female

Tipus	Descripció
Mascle	Rosca exterior
Dona	Rosca interna
Mascle × Mascle	External threads on both ends
Femení × Femení	Internal threads on both ends
Mascle × Dona	Mixed thread ends

A thread identification kit containing pitch gauges, a caliper, and reference profiles is worth the investment if you regularly handle mixed-standard fittings.

Measure a Brass Pipe Fitting

How to Choose the Right Brass Fitting Size

Once you understand what the size number actually means, selection becomes systematic. Run through these seven checks before placing an order:

Comproveu	Question to Ask
Pipe Size	What is the pipe nominal size?
Fil estàndard	NPT, BSPP, BSPT, o mètrica?
Connexió	Mascle o femella?
Pressió	What working pressure is required?
Temperatura	What operating temperature?
Aplicació	Aigua, HVAC, gas, or industrial fluid?
Material	What brass grade is required?

Common brass grades for fittings include CW617N (CuZn40Pb2) for general-purpose plumbing and CW602N (CuZn36Pb2As) for dezincification-resistant applications in aggressive water conditions.

Brass Fittings in industrial applications

Common Mistakes When Choosing Brass Fitting Sizes

Error 1: Treating Nominal Size as Actual Diameter

A 1/2″ fitting does not necessarily have a 1/2-inch thread diameter.

Error 2: Measuring Only the Fitting Body

The body diameter does not identify the thread size.

Error 3: Ignoring NPT vs. BSP

A similar diameter does not mean the threads are compatible.

Error 4: Confusing BSPP and BSPT

Both belong to the BSP family, but one is parallel and the other is tapered.

Error 5: Ignoring Male/Female Configuration

A correct thread size is not enough if the connection gender is wrong.

Error 6: Selecting by Diameter Without Checking TPI

Two threads can have similar diameters but different pitches or TPI.

Encaix de llautó Size vs Pipe Size: Are They the Same?

No—and this is where the confusion peaks.

Especificació	Refers To
Fitting nominal size	Standard connection size label
Tub OD	Outside diameter of the pipe
Pipe ID	Inside diameter of the pipe
Thread OD	Actual measured thread diameter

A fitting marked 1/2″ does not have a 12.7 mm thread OD. In NPT, the 1/2″ size has a 0.840″ thread OD. In BSP, the 1/2″ size has a 20.955 mm major diameter. The nominal size is a matching reference, not a physical dimension.

Brass Fitting Size vs Pipe Size

Need Accessoris per a canonades de llautó for Your Project?

Need brass pipe fittings in specific sizes, estàndards de fil, or connection types? Share your required fitting type, mida nominal, fil estàndard, material, and application with our team. Luoyang Datang Energy Tech Co., Ltd will confirm the appropriate specification and provide a quote.

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