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#82 -- Common Types of Threads Used in Fire Hose and Fire Department Connections: NPT, NST, and More!

Posted by Jason Hugo and Anna Hartenbach on 11/9/2017 to Fire Department Connection
During a fire emergency, time is in short supply. Discrepancies between the fire department’s hose threads and the fire department connection can translate directly to a greater property or, even, life loss during the emergency. Understanding the threaded devices on your property will enable you to take adequate precautions, so you have the right connection when you need it most.

When threading devices, there’s more than meets the eye! Thread size, gender, and even manufacturing materials can play a role in device connections.

In this article, we’ll dive into thread standards and thread sizing. We’ll travel back into history to gain a better understanding of thread sizes, learn what standards are used today, and show you what solutions are available. If you already know what thread you need, feel free to jump on over and check out our full range of Fire Department Connections, fire hose, and fire hose adapters.

If you haven’t quite made your connection yet, keep reading!

What does thread size mean?

Thread size refers to threads per inch (TPI) and thread pitch. TPI comes from the number of threads per inch on fittings, nozzles, hoses, etc. Thread pitch denotes the amount of space between threads in millimeters.

When referring to threads, devices are often described as “male” or “female” and compatible items “mate.” The female item has internal threads, while a male item has external threads. When the thread types of two items match they “mate,” which just means that the two items fit together functionally. The outside diameter of the male (OD or ODM) is the measurement of the large portion of the diameter, and the inside diameter of the female (ID or IDF) is the measurement of the diameter of the pipe within the walls.

Devices with male threading on both ends are called a nipple. Devices with female threading on both ends are called a coupling – because they connect to male threads like a couple. However, there are “hermaphroditic” connections, meaning they have both male and female threads.

Talk about industry jargon!

Why are there different thread types and sizes?

European firefighting advancements throughout history have largely contributed to those made in America. After the development of the hand-operated pumping devices in the 1700s, the city of Philadelphia crafted wooden water mains to aid in firefighting efforts. Instead of hydrants, they used what was called fire plugs, and their hoses were made of leather and rivets. They connected their hoses to the fire plugs with couplings.

At that time, couplings were made by local blacksmiths. Because of this, the coupling threads were dependent on the capabilities of the blacksmiths within each community. Over time, manufacturers used differences in the thread to differentiate and create protections from competition. However, this often meant that neighboring communities had incompatible connections.

Leather Hose

The Great Baltimore Fire of 1904 gave rise to the need for thread standardization. The fire blazed for thirty hours after it started on February 7, 1904. Fire suppression teams came from Philadelphia, New York, Wilmington, Harrisburg, Chester, Altoona, Annapolis, and Washington, D.C. to support local efforts. Due to the variations in thread sizing, many of them were unable to connect their hoses to Baltimore hydrants. This helped result in the destruction of 1,526 buildings encompassing 70 city blocks.

What are the types of threads used in fire protection?

From the Great Baltimore Fire of 1904 came the development of National Hose (NH) thread. It is also known as National Standard Thread or “fire hose thread,” since it is the most widely adopted thread size in the country. The threads are considered to be “straight,” meaning they are consistent. NH thread is comprised of a female coupling mating with a male coupling to form a connection.

Despite its prevalence, there are still many thread standards in use across the country (as mentioned above) – and the rest of the world!

Today, many cities still use unique thread standards. Most notably, this includes: Chicago (Chicago Fire Department Thread and Chicago Hose Thread); New York City Fire Department thread; Cleveland, OH; Cincinnati, OH; Toledo, OH; Pittsburgh, PA; Detroit, MI; Denver, CO; Salt Lake City, UT; Richmond, VA; Raleigh, NC; Pittsburgh, PA; Louisville, KY; Phoenix, AZ; and more. (Just a note, at QRFS we either stock or have access to all these threads and more for fire hose adapters, certain valves, and certain FDCs. Contact us for your specific situation). One speculation is that some cities and municipalities still use unique threads to reduce equipment theft.

National Pipe Straight Hose Thread (NPSH or NPS) is similar to NH threads, as they have the same TPI, but they do not taper. Because of these similarities, a female NPSH coupling can mate with an NPT thread, but a male NPSH cannot mate with a female NPT. Male NPSH can only connect to NPSH.

How do variations in thread standards impact the fire industry?

For starters, the various thread standards within the fire industry lead to many inconsistencies across the country and even from one city to the next. In some instances, like the Great Baltimore Fire of 1904, these inconsistencies result in longer burn times, more damage, and less fluidity between departments.

Aside from fire departments and municipalities, manufacturers must provide supplies to meet the demands. For some thread types, like NYFD thread, the demand is consistent enough for manufacturers to keep supplies readily available. However, for other municipalities’ thread sizes, this can mean longer wait times during purchasing because items are made to order.

The variations in thread sizing and standards even trickle down to building managers and owners. Without knowing or understanding thread sizing or standards, many individuals in charge of facilities’ maintenance may unknowingly purchase items with incorrect thread size or even the wrong size FDC plugs, fire hose couplings, or adapters.

What solutions are available today?

Thankfully today’s market offers numerous solutions to solve thread incompatibilities for fire department connections (FDCs) and fire hose. These simple, yet elegant tools are a vital piece to add to your tool selection to ensure a smooth connection when it's most necessary.

When it comes to fire hose adapters, we have you covered at QRFS! We have Male x Male, Female x Male, Female x Female, and Brass Swivel Adapters. We stock 1 ½” and 2 ½” adapters, but have access to a full range of aluminum adapters in nearly any size you can imagine. In the instance that you need to reduce from a 2 ½” hose to a 2” hose, we have you covered with a 2 ½” to 2” adapter. Most options are available in both brass or aluminum. Don’t see your particular threads listed? We can get custom threads for you!

As a completely different solution to an odd-threaded FDC, we offer the Adjust-a-Plug. Although it looks similar to a break cap, it functions like a plug. It features two adjustable metal plates on the back that allow it to mate with your local thread. The front metal bolt permits the user to lock it into place in the FDC once it has been adjusted to the proper fit.

Click here to view our supply of FDCs, Fire Hose, and Hose Adapters!

Still have questions or concerns? Leave them in the comment section below or contact us here and we’ll do our best to answer them quickly.

This blog was originally posted by Jason Hugo and Anna Hartenbach at QRFS.com/blog on November 9, 2017. If this article helped you find your thread mate, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.

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