Getting the boquilla hexagonal wrong means thread mismatch, leaks, or a fitting that fails sooner than it should. Therefore, it is very essential to choose the right type for your needs. This guide explains hex nipple types, materials, thread options, sizes, and how to select the right hex nipple for your application.
What is a Hex Nipple?
A Hex Nipple is a short pipe fitting with male threads on both ends and a hexagonal (six-sided) center section between the threaded ends.
| Feature | Practical Value |
| Hex center for wrench gripping | Torque is applied to the hex flats, not the sealing threads |
| Male threads on both ends | Direct connection between two female-threaded ports – no additional adapters required |
| Straight-through internal bore | Minimizes flow restriction compared with internally restricted fittings |
| Separate hex and thread sections | Helps reduce thread damage during installation and maintenance |
The hex flats are the key distinguishing feature. During installation, the wrench grips the hex flats rather than the threaded ends, reducing the risk of thread damage and making the fitting easier to install or remove during maintenance.
Hex Nipple Types
The main types include standard hex nipples, long hex nipples, reducing hex nipples, and special pipe nipples.
Standard Hex Nipple – HN Series
The HN series is the standard hex nipple. Both ends are male-threaded. They can be the same size or different, depending on your connection needs. The hex section is sized to give you good wrench grip without adding unnecessary bulk. It handles the bulk of general-purpose piping jobs.
The HN series is available in multiple thread configurations including NPT × NPT, NPT × ISO Tapered (RT), NPT × ISO Parallel (RS), NPT × SAE, and NPT × Metric combinations. Standard sizes range from 1/8″ to 2″ NPT.
Working pressure (316SS, ambient temperature):
1/8″ NPT: 10,000 psig
1/4″ NPT: 8,000 psig
3/8″ NPT: 7,800 psig
1/2″ NPT: 7,700 psig
3/4″ NPT: 7,300 psig
1″ NPT: 5,300 psig
Long Hex Nipple – HL Series
The hexagonal mid-section of the HL series is longer than that of the standard series, providing a larger contact area for the wrench. This design is particularly useful in high-torque installation applications. The extended hexagonal face offers better leverage and a more secure grip for the wrench. It also allows the wrench to approach the joint from a wider range of angles in confined spaces.
Available standard lengths: 1.5″, 2″, 2.5″, 3″, 4″, and 6″
These are useful for bulkhead connections through thick walls, transitions between flanges and pipework, or any high-torque application where a standard hex nipple doesn’t offer enough grip.
Reducing Hex Nipple
Reducing hex nipples have different thread sizes on each end, allowing direct connection between two ports with different diameters without additional adapters.
Our HN series supports reducing configurations. Simply specify different thread sizes for each end. For example, SS-HN-MN8-MN4 gives you 1/2″ NPT on one end and 1/4″ NPT on the other.
Common applications: large-bore pipe to small-bore equipment, pressure gauge hookups, or any transition between different pipe sizes.
Special Pipe Nipples – SPN Series
For applications requiring custom lengths or non-standard configurations beyond standard, long, and close nipple options. The SPN series offers flexibility for specialized piping layouts where off-the-shelf nipples do not fit. Custom lengths and non-standard configurations are available.
Hex Nipple Materials
316 Stainless Steel offers the best corrosion resistance. Molybdenum content resists pitting and crevice corrosion. Use it for chemical, marine, saltwater, and aggressive media.
304 Stainless Steel costs less, still handles general industrial, food processing, and clean atmospheric conditions.
Acero carbono has high tensile strength for structural and general piping — zinc-plated for rust protection.
Latón won’t spark — good for pneumatics, water lines, and explosive environments. Aluminum is for lightweight and specialty applications.
| Material | Code | Bar Stock Standard | Forging Standard |
| 316 Stainless Steel | SS | ASTM A276 | ASTM A182 |
| 304 Stainless Steel | S4 | ASTM A276 | ASTM A182 |
| Acero carbono | C | ASTM A108 | ASTM A105 |
| Latón | B | ASTM B16/B453 | ASTM B283 |
| Aluminum | AL | ASTM B211 | ASTM B247 |
Hex Nipple Thread Options
The five thread standards listed below cover the vast majority of global piping systems.
| Thread Standard | Specification | Primary Market |
| TNP | ASME B1.20.1, SAE AS71051 | North America |
| ISO Tapered / BSPT | ISO 7/1, BS EN 10226-1, JIS B0203 | Europe, Asia |
| ISO Parallel / BSPP | ISO 228, JIS B0202 | European instrumentation |
| SAE (Unified) | ASME B1.1 | Hydraulics, automotive |
| Metric | DIN / JIS | Metric-system regions |
Common combinations:
- NPT × NPT – North American standard piping systems
- NPT × ISO Tapered – Cross-standard connections (US equipment × European piping)
- NPT × ISO Parallel – US threads × European straight-thread sealing
- NPT × Metric – US systems × metric equipment interfaces
- Metric × Metric – Full metric systems
Selection Guide
Selecting the correct hex nipple for your project can be broken down into three straightforward steps.
Step 1: Confirm Material
Base your material selection on operating conditions.
316 Stainless Steel: corrosive media, saltwater, high temperature
304 Stainless Steel: general industrial, food processing, clean atmosphere
Carbon Steel: structural, general piping (zinc-plated)
Brass: pneumatics, water lines, non-sparking
Aluminum: lightweight, specialty
Step 2: Confirm Thread Standard & Size
Check the mating port on your equipment or piping:
- North American equipment / US projects → NPT
- European equipment / European projects → BSPT (ISO Tapered) or BSPP (ISO Parallel)
- Japanese equipment → JIS (Metric)
- German equipment → DIN (Metric)
Also verify whether both ends are the same size (straight nipple) or different sizes (reducing nipple). When in doubt, consult the equipment manufacturer’s documentation or use a thread gauge to confirm.
Measure length from end to end. This includes both threaded sections and the hex center. Do not measure only the threaded part. The overall length (L) determines the distance between the two connected ports. Too short, you cannot reach. Too long, it will not fit.
Step 3: Verify Working Pressure
Once you have selected the material and thread configuration, confirm that the working pressure rating exceeds your system’s maximum operating pressure.
A few pressure rules to keep in mind: smaller size equals higher pressure – 1/8″ NPT 316SS handles 10,000 psig, while 1″ NPT drops to about 5,300 psig. 316 stainless steel ratings are approximately twice those of brass. Carbon steel and brass ratings are approximately 50% of 316SS ratings. Temperature reduces pressure capacity – for steam or hot oil service, use stainless steel and derate accordingly.
Always allow a reasonable safety margin between the rated pressure and your actual system pressure.
Part Number Naming Rule
Brief explanation of how to decode NPTLOK part numbers.
| Code Segment | Meaning | Options |
| Material | Material code | SS = 316SS, S4 = 304SS, C = Carbon Steel, B = Brass, AL = Aluminum |
| Series | Product family | HN = Hex Nipple, HL = Long Hex Nipple, CN = Close Nipple, SPN = Special Pipe Nipple |
| Hilo | Thread type | MN = Male NPT, RT = ISO Tapered, RS = ISO Parallel |
| Size | Size designator | 2 = 1/8″, 4 = 1/4″, 6 = 3/8″, 8 = 1/2″, 12 = 3/4″, 16 = 1″ |
Preguntas frecuentes
Q1. What exactly is the difference between a close nipple and a hex nipple? Which one should I use?
A close nipple has no hex section — you have to grip the threads directly with a pipe wrench. That damages the threads. A hex nipple gives you a hex center for wrench grip, so threads stay untouched.Use a hex nipple for instrumentation, high-pressure, or any connection that may need disassembly later. Use a close nipple only for low-pressure, permanent installations where space is extremely tight.
Q2. How much pressure can a hexagonal fitting withstand?
Depends on material and size. 316SS ratings (ambient temperature):
| Size | 316SS | Latón |
| 1/8″ NPT | 10,000 psig | 5,000 psig |
| 1/4″ NPT | 8,000 psig | 4,000 psig |
| 1/2″ NPT | 7,700 psig | 3,800 psig |
| 1″ NPT | 5,300 psig | 2,600 psig |
Q3. Can the length be customized?
Yes. Standard lengths: 1.5″, 2″, 2.5″, 3″, 4″, 6″. Custom lengths available. MOQ: 10 pieces. Contact us with your requirements.
Contáctenos
NPTLOK is a precision pipe fitting manufacturer serving instrumentation, hydraulic systems, chemical processing, oil & gas, and power generation industries worldwide.
Our manufacturing facility is ISO 9001:2015 certified, and we operate both bar-stock and forging production lines to ensure full in-house quality control. Critical products undergo 100% pressure testing before shipment. Every fitting is marked with the NPTLOK manufacturer name for full traceability, and all male threads are capped for protection during shipping and storage.
All external threads on NPTLOK hexagonal fittings are NPT standard rolled threads.
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