Guide to Fitting Types: BSP or NPT? Solve Measurement and Material Selection in 5 Minutes

One of the biggest time-wasters in plumbing and piping systems is the parts that look “tiny.” If the wrong fitting is chosen, the consequences are not small at all: leaks, difficult installation, stripped threads, incompatible connections, and rework. In other words, the job takes longer, costs more, and becomes a headache. In this guide, I am not going to make you memorize every type of fitting one by one. Instead, we will clarify the three things that actually matter on site: thread standard (BSP/NPT), size (inch-DN), and material selection (304/316, black steel, galvanized, brass, PVC, PPRC).

After reading this article, you will be able to look at a part in your hand and say, “Alright, this is what it is.” And when you are not sure, you will be able to use photos as support and quickly find the right product.

Thread Standard: BSP or NPT?

When choosing threaded fittings, the first thing to check is the thread standard. The two most common standards are BSP (Whitworth) and NPT. These two standards are not fully compatible with each other. A wrong match can lead to problems such as leaks, difficult tightening, and stripped threads.

• BSP (Whitworth): Commonly used in Turkey and Europe.

• NPT: More commonly used as an American standard and is known for its tapered thread form.

Quick check tip: If you are not sure, share a photo and measurement of the existing part with us. We can help you identify the correct BSP/NPT standard and size match. It is a lot cheaper than trying to guess and ending up with the wrong fitting.

Size Selection: How to determine the size of threaded fittings?

Threaded fitting sizes are generally expressed in inches ("). In practice, the most commonly used sizes are 1/2”, 3/4”, and 1”. Here is the critical point: although inch sizes and DN are often treated as if they were a one-to-one mathematical equivalent, in plumbing systems they are usually used as nominal (approximate) equivalents. That is why, for the correct selection, size + thread standard + connection type should always be checked together.

Inch – DN quick table

The table below is a quick reference for the most commonly used measurements:

Thread Size (inch)	Approx. DN (nominal)	Usage Note
1/4"	DN8	Small connections
3/8"	DN10	Small connections
1/2"	DN15	Most common plumbing size
3/4"	DN20	Common
1"	DN25	Common
1 1/4"	DN32	Medium diameter
1 1/2"	DN40	Medium diameter
2"	DN50	Large diameter
2 1/2"	DN65	Large diameter
3"	DN80	Large diameter
4"	DN100	Large diameter

Note: DN equivalents are "nominal." For exact compatibility, tooth standard + pitch measurement + connection type.

Material Selection: Which fittings material makes sense?

There is no single answer to the question, "Which one is the best?" The right material varies depending on the operating conditions of the system. Factors like humidity, chemical environment, temperature, pressure, and the purpose of the installation all influence the choice. The mini table below helps speed up the decision-making process.

Material

Advantage

Where is it suitable?

Stainless Steel 304

Good general corrosion resistance

Water, general industry, normal environments

Stainless Steel 316

More corrosion-resistant than 304

Chemical applications, salty/humid environments, harsh conditions

Black Steel Fittings

Durable, suitable for industrial use

Steam, industrial lines (in suitable applications)

Galvanized Fittings

Coating advantage against corrosion

General plumbing in suitable environments

Brass Fittings

Practical and widely used in plumbing

Sanitary plumbing, water lines (under suitable conditions)

PVC

Lightweight, easy to install

Cold water/infrastructure, suitable chemical lines

PPRC

Commonly used in plumbing

Clean water systems, suitable temperature/pressure conditions

n short:If you say, "The risk of corrosion is high," consider stainless steel (especially 316).

If you say, "General plumbing," solutions like brass/galvanized may be reasonable.

Types of fittings: Which are the most commonly used parts?

When people say fittings, hundreds of products may come to mind, but the ones most commonly used in the field are clear: elbows, tees, reducers, nipples, couplings/sockets, unions, and plugs/caps. If the line needs to change direction, an elbow is used. If a branch connection is needed, a tee comes into play. If a diameter transition is required, a reducer is the right choice. What matters here is not just the name of the fitting, but the actual line requirement and the connection standard.

Quick Decision Summary (Choose the Right Fitting in 3 Steps)

Thread standard: BSP or NPT?

Size: What is the inch size? What is the approximate DN equivalent?

Material: According to the operating environment (304/316, black steel, galvanized, brass, PVC, PPRC)

If you get these three steps right, choosing fittings will not be left to chance.

FAQ: Most Frequently Asked Questions About Fitting Selection

Can BSP and NPT be used together?No. They are not fully compatible, and using them together can cause leaks and installation problems.

Should I choose 304 or 316?304 is commonly used for general applications. 316 is more suitable for chemical, salty, and highly corrosive environments.

What DN is 1/2”?It is generally accepted as DN15. For an exact match, the thread standard and connection type should also be checked.

Where can I buy fittings in Bursa Nilüfer? Is shipping available across Türkiye?Astel Mekanik Tesisat supplies a wide range of fittings, including stainless steel, black steel, galvanized, brass, PVC, and PPRC fittings. The company provides sales and shipping throughout all provinces of Türkiye, especially Bursa/Nilüfer.

Explore Fitting Types:https://www.astel-mekanik.com/fittingscesitleri