You are in the hardware store looking to replace a valve located beneath the sink, and there is a label stating "3/4-inch FIP" on the package. There is another label of "3/4-inch MIP" nearby. You do not know if both of these will connect to each other and whether they both fit the pipe installed in the wall. This is a moment faced by almost every handyman and to get it wrong means leakages, stripped threads and additional trip to the store. FIP is one of the most widely-used labels regarding plumbing fittings in North America, and once you learn what it means everything becomes clear.
This guide has finally explained what FIP is, how FIP fittings are used, specifications of these fittings, where they are applied, difference between FIP and NPT fittings, MIP and IPS fittings, when FIP fittings are used, their materials, cost and brands making these fittings, using plain language along with real-life examples.
Brief answer: FIP refers to Female Iron Pipe; this is a plumbing fitting with internal threads designed to accommodate a male-threaded pipe or fitting (MIP). Technically, FIP does not necessarily mean that it is made from iron; FIP fittings can be manufactured using brass, stainless steel, PVC, CPVC, or copper. FIP threads are made in accordance with NPT (National Pipe Tapered) thread specification (ANSI/ASME B1.20.1), so FIP means a female NPT fitting.
Table of Contents
- What Does FIP Mean?
- How FIP Fittings Work
- FIP vs MIP: The Female/Male Relationship
- FIP vs NPT: Same Thread, Different Name
- FIP vs IPS: Iron Pipe Size Explained
- Common Uses of FIP Fittings
- Materials: What FIP Fittings Are Made Of
- Sealing: Does FIP Need Teflon Tape?
- Sizes & How to Identify an FIP Fitting
- Prices & Brands
- Frequently Asked Questions
- References
- Conclusion
What Does FIP Mean?
FIP refers to Female Iron Pipe. It denotes a type of plumbing fitting that can imply two things.
- “Female” means the fitting has internal threads like the inside of a nut. It means the plumbing fitting accepts a male fitting.
- “Iron Pipe” refers to the iron pipe system of measurement in which the threads have been measured based on IPS (Iron Pipe Size), and it does not mean that the fitting is made of iron specifically.
This means that a “1/2 inch FIP” fitting will have a ½ inch internal pipe thread and accept a ½ inch male pipe fitting. It can be compared to the “nut” side of a nut-bolt type of connection.
You might also come across the term FPT (Female Pipe Thread), or FNPT (Female National Pipe Tapered), which both mean the same thing but differ in names. Hardware stores tend to use FIP a lot, the catalogs will also say FPT, while the engineering specification will reference FNPT.
How FIP Fittings Work
An FIP fitting achieves a leak-free connection with tapered threads. The FIP thread has an NPT taper where the threads are not parallel. When the male fitting (MIP) connects with the FIP fitting, the taper functions; that is, the threads are locked tighter and tighter so that they form a good mechanical seal along with the sealant.
- The male fitting has either Teflon tape around it or some pipe dope.
- It gets screwed in manually, then tightened, and as the taper starts working, the threads tighten up together.
Thus, taper + sealant = non-leaking threaded joint. It is the industry standard for water lines, air compressor lines, gas supply lines, and HVAC connections in North America.
FIP vs MIP: The Female/Male Relationship
| Feature | FIP (Female Iron Pipe) | MIP (Male Iron Pipe) |
|---|---|---|
| Thread location | Internal (inside) | External (outside) |
| Function | Receives the male fitting | Inserts into the female fitting |
| Also known as | FPT, FNPT | MPT, MNPT |
| Common parts | Valves, couplings, adapters, unions | Nipples, pipe ends, male adapters |
| Thread standard | NPT (female) | NPT (male) |
The term "MIP" and "FIP" describe two components that create a union or connector item. In practice, we thus have the male NPT, which can be referred to as MIP or Male Iron Pipe. And, it has to be added that the thread of a female NPT fitting differs little from the one of the MIP. In other words, if there is a fitting sold under MIP name, it has the same nominal size as a coupling sold as FIP. And if you're wondering how these threaded ends fit into the wider world of pipe joints, our guide to what connects two pipes together covers every joining method from threads to clamps to welding.
FIP vs NPT: Same Thread, Different Name
One question that perplexes many is whether FIP and NPT are one and the same. The answer is: FIP employs NPT threads; it is the female variant of NPT.
- NPT refers to National Pipe Tapered and denotes a type of thread standard — i.e., the dimensional and taper specifications (ANSI/ASME B1.20.1). NPT fittings exist as both male and female fittings.
- FIP is the term used in the plumbing industry to refer to female NPT fittings.
- An MIP fitting is said to be a male NPT fitting.
So in essence "FIP vs NPT" is not a comparison worth making because for all intents and purposes, FIP is NPT (female). If a specification states NPT while a label in the shop says FIP, they are the same fittings which employ the same threads. The only difference to note is that NPTF refers to a high tolerance variant of NPT that is used to produce a leak proof seal without using tape in comparison to the regular NPT specifications.
FIP vs IPS: Iron Pipe Size Explained
The IPS or Iron Pipe Size is the traditional system for sizing either iron pipe or threaded fittings which fitted with it, and it is what the NPT sizing system is built upon. To clarify, here is how they relate:
- IPS refers to the nominal size (e.g. half, three-quarters, one inch, etc.) used by the pipe and the fittings. It denotes approximate size; thus, one can say that the IPS of 0.5 inch is not actually equal to the 0.5 inch for outer diameter.
- FIP refers to the Female Iron Pipe and denotes the size according to IPS.
- On some websites, the term Female IPS can be found. The meaning is the same.
Therefore, in a nutshell, IPS refers to size, NPS refers to size, NPT refers to the system whereby threads were made.
Common Uses of FIP Fittings
FIP fittings are used in places where a threaded link to a male piping is required like below.
- Residential plumbing: Shut-off valves for sink and faucet, toilet connections which usually consist of the valve body being FIP and the supply tube having MIP.
- Water heaters: Connection for hot and cold water.
- HVAC and hydronic systems: Pump connections.
- Couplings and unions used to connect two male piping ends.
- Adapters like the FIP-to-FIP, FIP-to-hose-barbs, FIP-to-compression and others connecting different types of systems.
- In tanks and devices where FIP ports could be found after connections of tanks and equipment like filters and pressure gauges.
- FIPs are also used in commercial and industrial applications.
Materials: What FIP Fittings Are Made Of
The term "Iron" in the name notwithstanding, FIP fittings are made from a variety of materials depending on the type of fluid and pressure involved:
| Material | Best For | Notes |
|---|---|---|
| Brass | Potable water, valves, residential plumbing | Most common; durable and corrosion-resistant; can contain lead-free alloys for drinking water |
| Stainless steel | Corrosive fluids, food & beverage, marine | Strongest option; higher cost; 304 and 316 grades |
| Galvanized steel | Gas lines, industrial water, high strength | Zinc-coated steel; heavy and strong |
| PVC / CPVC | Irrigation, drainage, low-pressure water | Cheap and chemical-resistant; lower pressure and temperature limits |
| Copper | Specialized plumbing and refrigeration | Less common for threaded FIP; usually soldered instead |
For drinking water, you need to go for lead-free brass; for food-contact or corrosive service, it should be stainless steel since the same applies to sanitary and hygienic pipe systems. If you're weighing metal options for a plumbing or process line, our comparison of brass vs stainless steel pipe fittings breaks down the strength, corrosion, and cost trade-offs.
Sealing: Does FIP Need Teflon Tape?
In almost all scenarios, this holds true. FIP (NPT) threads seal by means of wedging but still necessitate a thread sealant for filling of the minute rope-like opening between male and female threads. These could be:
- Teflon tape (PTFE): This can be applied around the male (MIP) threads around 3 to 5 times in the direction of tightening (clockwise when seen from the end). Note that Teflon tape is meant for male threads only and not for the female ones.
- Pipe dope/thread sealant paste: Use a brush on the male threads, which works well for bigger or metal-to-metal joints and for operations under high pressure.
- Combination: In the event of high-pressure operations, professionals often use both, i.e., tape and dope.
- Built-in seal: Some fittings like some valves and compression fittings may have an O-ring or a gasket, which makes it unnecessary to use tape.
Never over-tighten FIP joints because the tapered threads can break both brass and PVC fittings. Tighten them until firm, plus a quarter turn (if metal) or as recommended by the manufacturer (if plastic).
Sizes & How to Identify an FIP Fitting
Common sizes of FIP fittings are 1/4", 3/8", 1/2", 3/4", and 1". The most frequently used sizes in a household system are 1/2" and 3/4". Here are some methods to tell whether a fitting is a female iron pipe fitting (FIP):
- Examine the inside of the fitting: If you see threads inside, it is FIP. If you see threads on the outside of the fitting, then it is male iron pipe (MIP).
- Check for any labeling: Any mention of FIP, FPT, or FNPT would mean that it is a female NPT fitting.
- Note the size: For instance, a 1/2" FIP fitting will fit only the 1/2" MIP pipe.
When in doubt, take the fittings along with the male part to the store for testing.
Prices & Brands
FIP fittings are inexpensive. Typical retail prices:
| Fitting Type | Typical Price |
|---|---|
| PVC FIP coupling (1/2–1") | $0.50–$3 |
| Brass FIP adapter / coupling | $2–$8 |
| Brass FIP shutoff valve | $5–$15 |
| Stainless FIP fitting | $4–$15 |
| Galvanized FIP fitting | $2–$10 |
| FIP hose-barb or specialty adapter | $3–$12 |
Some of the companies that make quality FIP/threaded fittings are SharkBite (push-to-connect + threaded), American Standard, Wattsm Mueller, Apollo, Sioux Chief, Nibco, and Mueller Industries for brass; Charlotte Pipe for PVC/CPVC; and Dormont, Parker, and Dixon for specialty and industrial threaded fittings. Manufacturers like Eagle Fittings offer sanitary-grade stainless steel fittings for stainless threaded fittings and sanitary systems.If you're new to the sanitary side, our overview of what a sanitary fitting is explains how hygienic connections differ from standard threaded plumbing.
Frequently Asked Questions
Can I connect FIP to NPT?
Yes, an FIP fitting is actually a female NPT fitting, so it fits perfectly with a male NPT (MIP) fitting of the same size. "FIP" is just how the plumbing industry refers to the female NPT fitting. The one distinct feature of an FIP fitting is that it uses 1/2-inch threads to fit a 0.5-inch male NPT pipe or nipple and is taped with Teflon tape or pipe dope. However, one must be careful with FIP fittings that have straight threads or follow different thread standards like BSP or metric threads, as they do not guarantee a proper fitting with an NPT thread.
What is the difference between FIP and NPT fittings?
That’s correct — there’s no distinction in terms of standards since FIP fittings have NPT threads. The difference lies only in the name of the standards in question as NPT stands for National Pipe Tapered whereas FIP (Female Iron Pipe) is the plumbing name for NPT fitting in the female version (also called FPT or FNPT). As for the male version, it is MIP (Male Iron Pipe). Therefore, it can be said that the difference between FIP and NPT is the same as the difference between a sedan and a four-door car because FIP is an FIP fitting.
Does FIP need teflon tape?
In almost every situation, it is correct. FIP (female NPT) threads seal by taper wedging, but they require a sealant to fill the spiral gap, such as Teflon tape or pipe dope on male (MIP) threads before screwing it into the FIP fitting. Use tape in the tightening direction, preferably applying at least three to five wraps or putting pipe dope on the male (MIP) threads; this way, it will provide adequate sealing even for applications with higher pressure. However, there is a limitation: if the joints come with built-in O-rings or rubber seals, tape is not necessary.
What is the difference between FIP and IPS?
IPS (Iron Pipe Size) is the designation for the nominal sizing system (1/2", 3/4", 1", etc.) used for iron pipe and iron pipe fittings. FIP (Female Iron Pipe) refers to its gender designation, which means a fitting with internal threads made according to the iron pipe sizing system or it can also be termed as Female IPS sometimes. IPS indicates “what sizing system?” while FIP indicates “what gender (female)?” Therefore, a fitting is called 3/4 inch if it is 3/4 inch FIP fitting which is made in 3/4 inch IPS female thread configuration.
References
- ASME B1.20.1 — Pipe Threads, General Purpose (Inch): the NPT standard
- IAPMO — plumbing code and threaded fitting requirements
- GageRef — NPT Thread Names Explained: MIP, FIP, MPT, FNPT
- Sannke — NPT vs FIP vs MIP: The Ultimate Thread Comparison Guide
- EngineerFix — What Is an FIP Fitting? Female Iron Pipe Explained
- NFPA — gas and fire safety standards for threaded pipe connections
Conclusion
FIP, which stands for Female Iron Pipe, refers to the internal-thread female component found within the conventional North American tapered pipe connection. It employs NPT threads along with MIP (maleficent abbreviation used for male fittings) hardware, and is available in brass, stainless steel, PVC, copper, and galvanized metals. The application through which one recognizes the type of connection to establish is called IPS or Iron Pipe Size. Various abbreviations, FIP, MIP, IPS etc., only represent various aspects of the same family of connections.
Thus, the practical stipulations dictate that an individual must seek the female gender by simply looking inside. This means that if the threads are located toward the interior, the connection is recognized to be FIP. Close attention must also be paid to the size when making connections; the sizes must match; it is must be also bourn in mind to use sealant for the male thread connection when making the connection. In addition, one must not tighten the connection too strongly. When discussing similar issues, one must also bear in mind that some connections are bacteria free, usually found in such industries as food production, pharmaceuticals, beverages etc.
