FDC Plug Doesn't Fit!

My FDC plug doesn't fit and I don't know why.

Don't panic. There are a few very common reasons your seemingly correct FDC plug doesn't fit:

1. Incorrect sizing

2. Incorrect or incompatible threading

3. Improper installation

Let's review each issue and run through some steps to address them.

Incorrect Sizing

Sizing FDC plugs is where many people run into problems. They come in three standard sizes that reflect fire department connection (FDC) sizes:


- 2-1/2 in. which is the most common BY FAR

- 3 in. which is for select jurisdictions such as New York City, San Francisco + more

- 1-1/2 in. which are typically in single inlet and/or residential systems.

You can determine what size you need by measuring the FDC, but only if it’s done correctly. If you place a tape or ruler on the outer diameter of the hole (the FDC’s swivel), the number will be too large:

The outside diameter of this swivel on a 2-1/2 in. FDC measures 3-1/2 in. (right), whereas the inner waterway’s diameter is 2-1/2 in. —the inner waterway is the correct size for a plug.

You can also verify the number by measuring the outer diameter and doing an approximate conversion:


- An outer swivel diameter of about 3-1/2 in. should need a 2-1/2 in. plug
- An outer swivel diameter of over 4 in. should need a 3 in. plug 
- An outer swivel diameter of about 2-1/2 in. should need a 1-1/2 in. plug

Incorrect or Incompatible Threading

If you are confident that you have the correct size plug and it still doesn't fit, you may need to take a look at the threading.

While most jurisictions use National Standard Thread (NST), there is a chance that your area uses a specialized thread for your FDC and hose connections. The list below are all areas that may have their own special thread:

- New York City (commonly known by New York Fire Department, or NYFD, threads)

- Chicago (commonly known by Chicago Fire Department or Chicago Hose thread)

- Cleveland, OH

- Cincinnati, OH

- Toledo, OH

- Pittsburgh, PA

- Detroit, MI

- Denver, CO

- Salt Lake City, UT

- Richmond, VA

- Raleigh, NC

- Louisville, KY

- Phoenix, AZ

If you are not in one of these cities, chances are you simply need NST threading. If you are located in one of the listed cities and your plug isn't fitting, you will need to order special threading.

View our selection of NST plugs.

View our selection of NYFD plugs or contact us to order special threads for other cities.

Improper Installation

Installing FDC plugs is a relatively simple process, but if you've followed the previous steps and are sure you have the correct plug, it's time to troubleshoot two areas:

- Debris in the FDC thread itself or the Plug

- Damage to the thread from forced installation

If there was debris inside of the threads on either component, sometimes forcing the install can cause thread damage. Even if the threads remain intact, it may be impossible to screw in a plug when there is debris blocking the connection.


Follow these steps to properly install an FDC plug:

1. Remove the old plug if it’s still there. If the part was properly installed, you’ll need to loosen it with a spanner wrench before twisting it out by hand.


2. Look inside the hole of an exposed FDC swivel and make sure there is no visible debris. If you spot anything, remove it.


3. Twist the new plug into the hole until it meets firm resistance, and then tighten it with a spanner wrench. If there are any issues here, you likely have the wrong size and/or threads.


4. Hook up an attached chain (if present) into the links on another plug chain (if the FDC has multiple swivels) or the eyelet/grommet on the FDC’s body.

It's a Fit!

That's it! If you've followed all three of these steps, you should have been able to identify the issue and correct it accordingly.

View our full selection of Plugs and Breakable Caps.