Pipe Locknuts For Steam | McMaster-Carr

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How to Identify and Measure Fittings

Pipe size is an industry designation, not the actual size. View information about how to measure threaded and unthreaded pipe and pipe fittings.

Low-Pressure Stainless Steel Threaded Pipe Fittings

Use these fittings in a low-pressure pipe line.

Fittings that meet ANSI/MSS SP-114 adhere to high-quality standards for heat treating, material thickness, and marking. 304 stainless steel fittings have very good corrosion resistance. 316 stainless steel fittings have excellent corrosion resistance.

Locknuts thread onto the male end of a fitting to provide extra holding power so the fitting won’t loosen from vibration. Locknuts that meet DIN 431 comply with international standards for pipe fitting locknut dimensions.

NPTF (Dryseal) threads and NPSL (National Pipe Straight Locknut) threads are compatible with NPT threads.

For technical drawings and 3-D models, click on a part number.

Locknuts

For Use With: Air, Natural Gas, Oil, Steam, Water
Pressure Class:
NPSL: 150
Fabrication:
NPSL: Heat Treated
Specifications Met:
NPSL: ANSI/MSS SP-114, ASTM A351
BSPP: DIN 431
Pipe Nipples and Pipe:
NPSL: Use Schedule 40 stainless steel
Flanges:
NPSL: Use Class 150 stainless steel

			304 Stainless Steel		316 Stainless Steel
Pipe Size	Max. Pressure	Max. Steam Pressure		Each		Each
NPSL Female
1/8	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
1/4	300 psi @ 72° F	150 psi @ 350° F	00000000	0000	00000000	0000
3/8	300 psi @ 72° F	150 psi @ 350° F	00000000	0000	00000000	0000
1/2	300 psi @ 72° F	150 psi @ 350° F	00000000	0000	00000000	0000
3/4	300 psi @ 72° F	150 psi @ 350° F	00000000	0000	00000000	0000
1	300 psi @ 72° F	150 psi @ 350° F	00000000	0000	00000000	00000
1 1/4	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
1 1/2	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
2	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
2 1/2	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
3	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
4	300 psi @ 72° F	150 psi @ 350° F	00000000	00000	00000000	00000
BSPP Female
1/8	Not Rated	Not Rated	00000000	0000	000000	00
1/4	Not Rated	Not Rated	00000000	0000	000000	00
3/8	Not Rated	Not Rated	00000000	0000	000000	00
1/2	Not Rated	Not Rated	00000000	0000	000000	00
5/8	Not Rated	Not Rated	00000000	0000	000000	00
3/4	Not Rated	Not Rated	00000000	0000	000000	00
1	Not Rated	Not Rated	00000000	00000	000000	00

Low-Pressure Iron and Steel Threaded Pipe Fittings

Use these fittings for low-pressure applications in noncorrosive environments.

Locknuts thread onto the male end of a fitting to provide extra holding power so the fitting won’t loosen from vibration. Some meet DIN 431, which is an international standard for pipe fitting locknut dimensions.

NPTF (Dryseal) threads, NPSC (National Pipe Straight Coupling) threads, and NPSL (National Pipe Straight Locknut) threads are compatible with NPT threads.

For technical drawings and 3-D models, click on a part number.

Locknuts

For Use With: Air, Natural Gas, Oil, Steam, Water
Pressure Class:
NPT: 125
NPSL: 150
Specifications Met:
NPT: ASME B1.20.1, ASME B16.4
NPSL: ASME B16.14
BSPP: DIN 431
Pipe Nipples and Pipe:
NPT, NPSL: Use Schedule 40 steel

NPT Female
Pipe Size	Material		Each
3	Iron	000000000	000000
NPSL Female
1/8	Steel	000000000	0000
1/4	Steel	000000000	0000
3/8	Iron	000000000	0000
1/2	Iron	000000000	0000
3/4	Iron	000000000	0000
1	Iron	000000000	0000
1 1/4	Iron	000000000	0000
1 1/2	Iron	000000000	00000
2	Iron	000000000	00000
BSPP Female
1/8	Steel	0000000	0000
1/4	Steel	0000000	0000
3/8	Steel	0000000	0000
1/2	Steel	0000000	0000
3/4	Steel	0000000	0000
1	Steel	0000000	00000
1 1/4	Steel	0000000	00000
1 1/2	Steel	0000000	00000
2	Steel	0000000	00000

Low-Pressure Galvanized Iron and Steel Threaded Pipe Fittings

The galvanized finish on these fittings provides fair corrosion resistance. Fittings are for use in low-pressure applications.

Locknuts thread onto the male end of a fitting to provide extra holding power so the fitting won’t loosen from vibration.

NPSC (National Pipe Straight Coupling) threads and NPSL (National Pipe Straight Locknut) threads are compatible with NPT threads.

For technical drawings and 3-D models, click on a part number.

Locknut

For Use With: Air, Steam, Oil, Water, Natural Gas
Pressure Class: 150
Specifications Met: ASME B16.14
Pipe Nipples and Pipe: Use Schedule 40 galvanized steel
Flanges: Use Class 150 galvanized steel

NPSL Female
Pipe Size	Material		Each
1/4	Galvanized Steel	00000000	00000
3/8	Galvanized Iron	00000000	0000
1/2	Galvanized Iron	00000000	0000
3/4	Galvanized Iron	00000000	0000
1	Galvanized Iron	00000000	00000
1 1/4	Galvanized Iron	00000000	00000
1 1/2	Galvanized Iron	00000000	00000
2	Galvanized Iron	00000000	00000

Extreme-Pressure Steel Threaded Pipe Fittings

The strongest steel fittings we offer, these can withstand extreme-pressure applications.

Galvanized and zinc-plated steel fittings have better corrosion resistance than plain steel fittings. PTFE-coated steel fittings have better corrosion resistance than galvanized and zinc-plated steel fittings.

Locknuts thread onto the male end of a fitting to provide extra holding power so the fitting won’t loosen from vibration.

For technical drawings and 3-D models, click on a part number.

Locknuts

For Use With: Air, Hydraulic Fluid, Natural Gas, Oil, Steam, Water
Temperature Range: -100° to 500° F
Pipe Nipples and Pipe: Use Schedule XXH steel
Flanges: Use Class 1500 steel

NPT Female
Pipe Size	Dash Size	Max. Pressure	Max. Steam Pressure	Material		Each
1/8	02	10,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	000000
1/4	04	10,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
3/8	06	10,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
1/2	08	10,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
3/4	12	5,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
1	16	5,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
1 1/4	20	5,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
1 1/2	24	3,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	00000
2	32	3,000 psi @ 72° F	5,000 psi @ 500° F	Galvanized Steel	0000000	000000

Low-Pressure Plated Brass Threaded Pipe Fittings

Used in low-pressure pipe lines, these brass fittings have a plating that makes them shiny and improves corrosion resistance.

Chrome-plated brass fittings are shinier and withstand corrosion better than nickel-plated brass fittings.

Locknuts thread onto the male end of a fitting to provide extra holding power so the fitting won’t loosen from vibration.

For technical drawings and 3-D models, click on a part number.

Locknuts

For Use With: Air, Natural Gas, Oil, Steam, Water
Pressure Class: 125
Specifications Met: ASTM B456
Pipe Nipples and Pipe: Use Schedule 40 brass

NPT Female
Pipe Size	Max. Pressure	Max. Steam Pressure		Each
Chrome-Plated Brass
1/8	200 psi @ 72° F	125 psi @ 400° F	00000000	000000
1/4	200 psi @ 72° F	125 psi @ 400° F	00000000	00000
3/8	200 psi @ 72° F	125 psi @ 400° F	00000000	00000
1/2	200 psi @ 72° F	125 psi @ 400° F	00000000	00000
3/4	200 psi @ 72° F	125 psi @ 400° F	00000000	00000
1	200 psi @ 72° F	125 psi @ 400° F	00000000	00000