What Is a Female Compression Nut
A female compression nut is the threaded collar that drives the ferrule onto the tube and holds the joint together. Its 45 degree internal seat pushes the ferrule forward until the ferrule grips the tubing. For metric lubrication lines, see 6 mm compression nut fittings. Imperial tube sizes from 1/4 to 3/4 inch stay on this page. The nut is one part of a three-part joint: nut, ferrule and body. This page lists the nut only. Brass C36000 or C69300, with a C46400 naval brass option, keeps the nut stable on copper, PEX, PE and CPVC lines.
Sizes and Threads
Size is chosen by tube outside diameter, not by thread. Wall thickness ranges from 0.032 to 0.083 inch across the range, and the ferrule seat OD runs from 0.375 to 0.875 inch.
| Tube OD (inch) | Hex (inch) | Female Thread (inch) |
|---|---|---|
| 1/4 | 7/16 | 1/8 |
| 5/16 | 1/2 | 1/8 |
| 3/8 | 9/16 | 1/4 |
| 1/2 | 3/4 | 3/8 |
| 5/8 | 7/8 | 1/2 |
| 3/4 | 1 | 1/2 |
Three thread types are available. FIP is a tapered internal thread that mates with an NPT male thread and seals on the threads themselves. NPSM is a straight mechanical thread that seals on a gasket or a seat, not on the threads. BSP is available on request. These thread types are not interchangeable.
Pressure and Temperature Ratings
Ratings depend on the tube material, because the tube and the ferrule grip carry the load. The table below lists working pressure at 73°F and the temperature limits for each tube type.
| Tube Material | Pressure at 73°F (PSI) | Continuous Max (°F) | Intermittent Max (°F) |
|---|---|---|---|
| Copper | 200 | 250 | 300 |
| PEX with insert | 160 | 200 | 210 |
| PE | 150 | 140 | 150 |
| CPVC | 180 | 180 | 200 |
All ratings step down as temperature rises above 73°F. Derate for elevated temperature service and stay inside the continuous limit for long-running lines.
Ferrule Options and Tube Materials
The ferrule does the sealing. Brass CDA 360 suits copper and brass tube. 316 stainless steel suits corrosive service and repeated thermal cycling. Acetal and nylon suit PEX and PE, and those two plastic tube types require an internal support insert so the tube wall cannot collapse under the ferrule. Never use a brass ferrule on PEX or PE. The ferrule is a single-use component: once compressed it is permanently deformed and cannot be reused. The nut itself can be reused if the threads and seat are undamaged. Related parts in this family include brass compression sleeves and ferrules and compression straight tube fittings. For background on how the three parts work together, see the ferrule and compression fittings technical guide.
Installation
Five steps make a reliable joint. Slide the nut onto the tube first, then the ferrule with its tapered end toward the nut. Push the tube fully into the body until it seats against the internal stop. Hand tighten the nut onto the body. Then hold the body with one wrench and turn the nut with a second wrench to the specified torque.
| Tube OD (inch) | Turns Past Finger-Tight | Recommended (ft-lbs) | Maximum (ft-lbs) |
|---|---|---|---|
| 1/4 | 1 to 1.25 | 6-8 | 12 |
| 3/8 | 1 to 1.5 | 10-14 | 18 |
| 1/2 | 1.25 to 1.5 | 15-20 | 25 |
| 5/8 | 1.5 to 1.75 | 20-25 | 32 |
| 3/4 | 1.5 to 2 | 25-30 | 40 |
These values assume clean dry threads; use the lower end for plastic tube. Four mistakes cause most problems: a reused ferrule, over-tightening, an angled cut, and a tube that never reached the internal stop. Cut the tube perpendicular with a tube cutter and deburr it fully before assembly.
What Is Supplied
Each order supplies the female compression nut only, in the tube size and thread type selected. Ferrules and fitting bodies are ordered separately. Applications include residential plumbing, HVAC refrigeration and condensate, compressed air, irrigation, pneumatic and coolant lines, and marine freshwater with naval brass. These nuts are not for strong acids below pH 3 or strong alkalis.
Frequently Asked Questions
What is a female compression nut?
It is the threaded collar that drives the ferrule onto the tube. Turning it compresses the ferrule against the tubing.
Is this listing the nut, the fitting or the ferrule?
A compression joint has three parts: the nut, the ferrule and the body. This listing is the nut only.
How do I choose the right size?
Choose by tube outside diameter, never by thread size. Common pairings are 1/4 inch tube with a 7/16 hex.
Can a ferrule be reused?
No, the ferrule is permanently deformed once compressed. The nut can be reused if undamaged.
How tight should the nut be?
Tighten finger-tight, then add the listed turns with two wrenches. Do not exceed the maximum torque for the size.
What is the difference between FIP and NPSM?
FIP is tapered and seals on the threads. NPSM is straight, sealing on a gasket or seat.
Can these nuts be used with PEX?
Yes, with a plastic ferrule and an internal support insert. Never use a brass ferrule on PEX or PE tubing.
Why does the joint leak?
Common causes are under-tightening, over-tightening, a reused ferrule, an angled cut, or a tube short of the stop. Correct each before reassembly.
Can these nuts be used with stainless tubing?
Stainless tubing is not listed for these nuts. The declared tube materials are copper, PEX, PE and CPVC; confirm before ordering.
Who supplies these compression nuts?
IsoHiTech Lubrication Systems, founded in 2023, engineering since 2006, builds and supports every unit. Email inquiry@isohitech.com for specifications and a quotation.
Send your tube size, thread type and ferrule material through the quote request page. For larger projects, the same contact form reaches our team directly.
