4 Steps to Choosing Your Fifth Wheel Pin Box

Your fifth-wheel's pin box, also called a king pin box, is a big part of your fifth-wheel towing experience, even though you might not realize it.

It affects how comfortable (or not comfortable) the ride is if you don't have a cushioned pin box, and it can also allow you more turning clearance if you have a shorter truck bed. And like all things, your pin box may eventually need to be replaced for a variety of reasons.

There are a few reasons why you might need to replace your pin box. Maybe you're feeling frustrated because your fifth wheel's pin box was just damaged and needs to be replaced in order to safely tow your fifth wheel. Maybe your current pin box is technically fine, but it has no cushion or shock absorption (giving you the most uncomfortable ride imaginable). Or maybe you have a truck bed shorter than 8 ft, and you're tired of having to get out of your truck to slide back your fifth-wheel hitch every time you make a sharp turn, so you want to switch to a Sidewinder pin box.

If you relate to any of these scenarios, don't worry. We'll help you figure out all the information you need to choose and then replace your pin box and make sure that it will last you a long time.

What's the difference between a pin box and a king pin?

Bolted to the front of your fifth wheel, the pin box is the entire piece that connects your fifth wheel to the fifth-wheel hitch in your truck bed. The bottom portion of the pin box is typically referred to as the king pin; this is the circular piece that slides into the u-shaped portion of your fifth-wheel hitch.

Pin boxes come in all different shapes and sizes. If you have a short bed and don't already have a sliding fifth-wheel hitch, you can get a Sidewinder pin box. A Sidewinder pin box has a rotating turret that will automatically move back when turning to give your truck more turning clearance. These are great because instead of having a sliding fifth-wheel hitch where you have to get out of your truck every time you make a 90 degree turn, you can stay in the comforts of your truck the whole time with no worries.

For an extremely comfortable ride, you can get a cushioned pin box with shock absorbers. These types of pin boxes will reduce the chucking and jarring that you'll usually feel while towing, so much so that you will probably forget your fifth wheel is even behind you!

How to Replace Your King Pin Box

Pin boxes are a custom-fit item; however, there's no way to determine which one you need based on the year, make, and model of your trailer (like you would with a custom-fit hitch).

The easiest way to replace your pin box is to find the pin box's manufacturer name along with its specific pin box number. These are both typically located on a sticker on the pin box or on the king pin itself. This pin box number will usually be 3-4 numbers long and can have letters attached to it. Some very common pin box numbers are Lippert's 1621, 1716, and 1116 pin boxes.

Over time this number can seem to magically disappear (crazy how that happens, right?), so you may not be able to locate this information anymore. If you're lucky and your trailer's manufacturer is still in business, you may be able to give them the VIN number of your fifth wheel so that they can cross-reference what your pin box number is. If not, there's still another way to determine what your pin box number is so that you can replace it.

You can measure your bolt pattern to find a correct replacement. There are 4 steps to measure your pin box and determine what pin box number you have:

Find your pin box style using our guide below (short, medium, long, or telescoping).
Measure your existing pin box's bolt pattern using our simple guide.
Determine your pin box number based off those measurements using the charts below.
Choose, purchase, and install your new pin box.

Keep reading, I will describe these steps in further detail and tell you exactly how you can replace that ol' hunk of metal on your fifth wheel with a shiny, new pin box.

Step 1. Find Your Pin Box Style

First, find the pin box style from the drawings below that matches the pin box on your 5th wheel trailer. There are five different types of pin box stlyes: short, medium, long, telescoping (45 degrees), and telescoping (72 degrees). The medium and long styles are the most popular for most modern fifth wheels.

Step 2. Measure Your Existing Pin Box

Next, after you have selected your pin box style, click on the drawing below that matches it. Then print out the drawing and take it to your trailer.

Use the drawing to measure the horizontal bolt hole distance, vertical bolt hole distance, bolt size, bolt head size, front row of bolts to king pin, back row of bolts to king pin and pin box width. Also, record the number of bolts per side that secure the pin box to the trailer frame.

Click on your pin box style to access a printable full size drawing.

Click to enlarge

Step 3. Determine Your Pin Box Number Based off Your Measurements

Now, find the drawing of your pin box style again. Use the pin box measurement chart that corresponds to your style to match the measurements of your trailer's OEM pin box to the manufacturer and model number. This will be the proper replacement pin box for your 5th wheel.

Note: Extending a pin box increases the amount of leverage applied to the frame of a 5th wheel trailer. Because this increased leverage can cause damage to a trailer frame, trailer manufacturers might not honor the trailer warranty if the pin box has been extended. Check with your trailer manufacturer if a new pin box will add more than 6" to the length of your original.

Step 4. Purchase and Install Your New Pin Box

After you have found and purchased your new pin box, it's time to get it installed!

Pin boxes aren't hard to install, but these giant hunks of metal can be heavy. So grab a friend or two, even if you have to bribe them with pizza and drinks, and get your tools together. Typically, all you will need for the installation will be a drill with the correct sized sockets and a torque wrench. Follow the specific installation instructions on how much you should be torquing down the bolts.

If you'd like to see how the installation is done, click here to see a video on the installation of a Reese 5th Airborne Pin box.

Still have questions?

Give our experts a call at 800-298-8924, or contact us online. We're happy to assist any way we can!

About the Author

My journey with etrailer started in Customer Service, where I went through months of product training to make sure that I had all of the knowledge I needed to help our neighbors find a solution to any situation. I helped them with technical questions, troubleshooting, product information, and anything else they needed. Since it has always been my passion to write and express myself through words, I made the transition over to the content side of the website so I could combine my product knowledge and passion for writing.

In order to make sure that I am giving you the most accurate, current information, I am constantly doing research and talking with people who are doing what I am writing about every day. I am constantly striving to find out what questions you are asking, and to give you an answer to every one of those questions, plus answers to questions you haven't even asked yet - yes, I'm that good. I am consistently getting hands-on experience with our products, and training with our vendors to ask them all the hard questions, that way you can have all of the information you need before making a decision.

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Questions and Comments about this Article

Ming D. 2/15/2021

Respect. This is excellent, readable, tech-level work. Organized and clear. Have you considered doing an article about 5th wheel couplings that cause the RV to be angled upwards at the nose instead of level / in-line with the height of the truck? If you have the data, would you direct me, please.

Reply from Jon G. 2/16/2021

Thank you for the compliments! We have an article that talks about how to choose the correct 5th wheel hitch for your application which I am linking for you to check out. If you aren't able to lower the front of your RV and still retain that 5" - 6" bed side clearance that the article talks about then you might need to look into increasing the height of your RV. Let me know if this is the case and I can help you look into this as well.

Helpful Links

faq-fifthwheel.aspx

Philip G. 2/12/2021

I have a 1979 Holiday Rambler Presidential 30' fifth wheel camper. It has what has been described as an inverted fifth wheel hitch: the fifth wheel plate is on the trailer, and the king pin is in the bed of the tow vehicle. I have the king pin adapter for a B&W turnover ball hitch system, but would like to replace the box on my camper with a conventional king pin box. Advice on parts or on how to locate a fabricator to weld up a new box would be appreciated. Thanks,

Reply from Jon G. 2/12/2021

That is an interesting setup. Does the pin box have any numbers on it (like 1620 or 0719)? That would be the first step.