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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Written by: Olivia M.

Andrew N.

9/27/2023

Wow, this is cool.

Andy N.

9/27/2023

@AndrewN Wow, it sure is.

Mike L.

9/27/2023

@AndrewN We're glad you found it helpful!

Mike L.

9/27/2023

@AndyN Awesome. We're glad it helped you!

John C.

9/15/2023

I need to replace my 45 degree pin box on our 2000 Travel Supreme because the pin broke loose but can't find anything.

Mike L.

9/16/2023

@JohnC In order to recommend a replacement, I'll need to know the model number of your existing pin box. There should be a plate or sticker on the pin box that will have that information.

John C.

9/16/2023

@MikeL Fabex model #316 Part# 219-293-0717

John C.

9/17/2023

@MikeL that link was useless. That's why I reached out to you for assistance.

See All (4) Replies to John C. ∨

Daniel R.

5/11/2023

I am looking at buying the 2019 grand design 337rls GVWR is 13,998 I was thinking about putting the Resse 20K gooseneck on and wonder what are the advantages and disadvantages to it are VS. say the Gen Y pinbox

Paul S.

5/4/2023

Why would you want to replace your pin box?

Vivian

7/26/2022

I have a 2018 grand design 303rls GVWR is 11,999 and has a solid 1621 pin box. My hitch is a Demco Recon. For the most part the towing experience is fine and smooth. But the roads are getting worse and sometimes I get chucking when going over these bad areas. What would be best pin box option for helping out when going over these areas?

David B.

7/26/2022

I will give you my two favorites, the Gen-Y # 325-GH-8040 is very much a hands off long lasting unit that needs minimal maintenance. It does need a pin weight between 1.5k and 3.5k but if your trailer is 12k you should be around 2,400 lbs on the pin. The Curt # LC328492 is an adjustable air bag system that needs to be monitored and adjusted but offers a quality ride on rough roads. Both units are made in America, Curt has a 1 year warranty and Gen-Y has a 5 year warranty.

Vivian

7/26/2022

@DavidB I was considering the MoRyde and RotoFlex mostly because shock absorption is not as much as issue as chucking. Since the Demco Recon has a pivoting head, wondering if that would make the RotoFlex work more efficiently? My pin weight is 2470 lbs.

David B.

7/26/2022

Those two that I linked work great for chucking and you did ask for the best lol and the Flex Air is great. The Rota-Flex will help minimize some chucking but it won't be as good as or better than the Gen-y or the Flex Air. That's not an upsell either, it's a good item just not better or best.

Al S.

11/12/2021

Al Sray <[email protected]> please help me select a pin box. I have a 1621 hd 18,000# stock pin box. Pr. No. 1191151, measures 17 3/4 x 25 5/8.Would like to purchase a morryde rubber pin box pt. No. Mr84vr, measures 17 3/4 x 25 5/8,or a lippert flex air pin box. Pt.no.328492, Witch one is better? I see a lot of morryde pin box on fifth wheel trailers at camp grounds, but not a single lippert flex air, why? Flex air is double in price and weighs 100# more. Is that the reason or is a morryde pin box better? I would like to purchase the best for my fifth wheel. I also have a curt slider hitch with slide bar jaw, and a 6 1/2 ft short bed. My trailer weight loaded is 9,000# There are two measurements on line for the 328492 flex air, one is 17 3/4 x 25 5/8, the other is 20 3/4 x 28 3/4, what measurement is correct? If pinbox is 20 3/4 x 28 3/4. 3 “ longer it may hit my tailgate when hitch is slid back. I believe the flex air pinbox would give me better performance, open for suggestions, any help At all please, thank you. Sent from my iPad

Les D.

11/15/2021

Thank you for your detailed information. As you have indicated that your trailers wing flanges have a 1621-HD bolt pattern, that filters your choices down to pin boxes with the same 1621-HD pattern. I have placed a link below with those choices. You have indicated that your 5th Wheel Trailer loaded is 9000 pounds. This seems a little light for a 5th wheel. Is that the GVWR as shown on the trailer sticker? If you only load it to 9000 pounds, but it CAN be loaded to 11,000 pounds, you should purchase the higher rated king pin box. I would double check this. If you would like a MorRyde cushioned pin box could use the MorRyde # MR64VR. The Lippert # LC328330 Rota-Flex is very similar to the MorRyde in that they both use a slab of rubber to cushion the ride. A big step up is the Lippert # LC158778 Air Ride king pin. This pin box has a large air bag inside of the box and an air shock at the end of the box. This model will offer the smoothest ride. As you mentioned, there are price differences. The higher costs are associated with higher tow ratings, and additional parts that deliver better performance. If it is in your budget, I would pick the Air Ride box. Regarding measurements of king pins and hitches – I have never heard of a pin box hitting a tailgate. Also, you mentioned “Flex Air,” but that was not one of the choices. If I misunderstood please let me know.

Helpful Links

s.aspx?qry=pin+box&furl=-pg-fifth_wheel_king_pin-co-lippert_1621hd

Les D.

11/15/2021

Helpful Links

s.aspx?qry=pin+box&furl=-pg-fifth_wheel_king_pin-co-lippert_1621hd