1. Fifth Wheel King Pin
  2. Lippert Components
  3. 1621
  4. Lippert
  5. Reduces Bounce and Jarring
  6. 21000 lbs GTW
Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs

Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs

Item # LC369535
lowest price pledge
Our Price: $1,495.06
Fifth Wheel King Pin
This item qualifies for Free Truck Freight Shipping
Shipping Weight: 232 lbs
In Stock
Lippert Components Fifth Wheel King Pin - LC369535
zoom in icon
zoom out icon
Comment field cannot be left empty.
Name field cannot be left empty.

Thank you! Your comment has been submitted successfully. You should be able to view your question/comment here within a few days.

Error submitting comment. Please try again momentarily.

Product Images

Flex Air drastically reduces chucking, absorbs road shock, and minimizes bounce. The internal air bag and built-in strut work with the rubberized pivoting head to achieve a dramatically smoother ride. Replaces Lippert 1621 pin boxes. Call 800-298-8924 to order Lippert Components fifth wheel king pin part number LC369535 or order online at etrailer.com. Free expert support on all Lippert Components products. Guaranteed Lowest Price and Fastest Shipping for Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs. Fifth Wheel King Pin reviews from real customers.
  • All Info
  • Reviews (4)
  • Q & A (77)
  • Videos (1)
  • Photos
  • Why etrailer?

Lippert Components Fifth Wheel King Pin - LC369535

  • 1621
  • Lippert
  • Reduces Bounce and Jarring
  • Lippert Components
  • 21000 lbs GTW
  • Pin Box Upgrade
  • Cushioned
  • Fixed Turret

Flex Air drastically reduces chucking, absorbs road shock, and minimizes bounce. The internal air bag and built-in strut work with the rubberized pivoting head to achieve a dramatically smoother ride. Replaces Lippert 1621 pin boxes.


  • Air ride pin box with a pivoting head replaces standard pin box on your 5th-wheel trailer to cushion your ride, improve handling, and limit strain on truck and trailer
    • Drastically reduces chucking
    • Virtually eliminates bounce and jarring
  • Internal air bag absorbs road shock
    • Scissor-like motion allows pin box to compress, compensating for jarring and bounce
    • Built-in shock ensures that pin box rebounds - keeps air bag from breaking down
  • Pivoting head limits chucking by allowing controlled movement of the king pin within your hitch
  • Rubber compound built into the head absorbs road shock
    • Reduces wear and tear on trailer
  • Black powder coat provides rust resistance
  • Sturdy steel construction
  • King pin connects to any 5th-wheel trailer hitch
  • Bolt-on installation with no assembly required
  • Made in the USA


  • Designed to replace Lippert 1621 5th-wheel pin box
  • Weight capacity: 21,000 lbs
  • Distance from bottom of king pin to top of box: 19-9/16"
  • Distance from center of king pin to back of box: 29-9/16"
  • 1-Year limited warranty


  • Do not use the Trailair Flex Air pin box with any type of gooseneck adapter.
  • Because of the size of this item, it ships via truck freight.

Getting there is half the fun, right? Not if you're being bumped, jerked, jammed, and pushed around from the chucking, road shock, and bounce that occurs as you tow your fifth-wheel trailer or RV. And imagine the costly wear and tear on your trailer as it endures that rocky ride.

Put the fun back into your trip and ease the stress on your trailer by replacing your factory pin box with the Trailair Flex Air pin box. The internal air bag and built-in shock work together to cushion your ride, improve handling, and limit strain on both your truck and your trailer. But what sets the Flex Air apart from other air ride pin boxes is the addition of a pivoting head. This head, along with its built-in rubber compound, provides additional cushion, absorbs road shock, and reduces chucking for a significantly improved ride.

Rubber Compound and Internal Air Bag Absorb Road Shock

Lippert Flex Air pin box has a rubberized pivoting head

A heavy-duty rubber compound is built into the head assembly of the Flex Air pin box. This rubber is the first defense against road shock. It helps to absorb the bumps and vibrations experienced when towing a fifth-wheel trailer over rough roads. Standard pin boxes without any type of shock absorption transfer road shock to your trailer, resulting in potential damage to the trailer and an overall bumpy ride. The shock-absorbing rubber inside the Flex Air takes the beating so there's less wear and tear on your trailer or RV and you get a smoother ride.

Lippert Flex Air pin box has a shock and air bag

Because the rubber may not be able to absorb all of the road shock that you experience, the Flex Air also implements air ride technology to virtually eliminate shock. When you encounter uneven terrain on your trip or hit a pothole on the highway, the Flex Air pin box compresses vertically, similar to how a pair of scissor blades closes in on each other. This compression transfers the road shock and vibrations to the internal air bag, saving your fifth-wheel hitch, trailer, and tow vehicle frame from enduring a rocky ride.

A built-in strut, or shock, controls the Flex Air's compression so that the internal air bag doesn't burst. The strut also causes the pin box to appropriately rebound without any bounce, and positions it to be ready for the next bump in the road.

Pivoting Head Reduces Chucking

Lippert Flex Air pin box has a pivoting head that reduces chucking

The pivoting head on Flex Air allows for controlled back and forth movement of the king pin to reduce the uncomfortable jarring known as chucking. Unlike a rigid pin box that has little give at the point where the trailer and the hitch are connected, the Flex Air can pivot slightly to compensate for those times that your trailer suddenly pushes or pulls on your tow vehicle. Because the pin box head - not the king pin itself - is moving, the chucking that often occurs when the king pin jerks around inside the hitch is significantly reduced.

Simple Setup and Installation

First, simply remove your existing Lippert 1621 pin box from your trailer. The Flex Air uses the same bolts that held on your original pin box so no additional hardware is required for installation. Plus, the Flex Air pin box comes out of the box ready to be put on your trailer, so no assembly is needed. Because the Flex Air is quite heavy, you should put it on an elevated surface or have a friend help you support its weight during installation.

The internal air bag should be inflated after the Flex Air pin box has been mounted on your trailer. Using the air intake valve, inflate the air bag until the outer cylinder of the shock rises high enough to fully expose the yellow inflation indicator sticker.

369535 Lippert Components (LCI) Flexair by Trail Air Fifth Wheel Kingpin Box for Lippert 1621 - 21,000 lbs

Installation Details LC369535 Installation instructions

Video of Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Lippert Components Fifth Wheel King Pin - Pin Box Upgrade - LC369535 Review

Speaker 1: Today, we're going to be taking a look the Trailair FlexAir fifth wheel pin box. This is going to be a really nice addition to your fifth wheel trailer because it's going to drastically reduce chucking and absorb road shock. It's also going to minimize bounce with your fifth wheel trailer. And the internal air bag and built-in strut work together with the rubberized pivoting head to achieve a dramatically smoother ride.This is going to replace the standard pin box on your fifth wheel trailer from Lippert. Lippert 1621 or one-six-two-one. And it's going to be designed, again, to ensure that smoother ride with the rubber compound built into the head.

If I turn the table here, I'll give you a little bit better look at that. So it's basically going to be a rubber block built into that head assembly and that's going to absorb a lot of that initial road shock. And then this plate is also going to pivot, so it's going to allow controlled movement of that head assembly within your hitch so it's going to reduce that chucking that you normally find with your fifth wheel trailer. Any road shock that's not absorbed between those two will be handled by the air bag that is built in. That's going to virtually eliminate any bouncing or shock that you would have from that trailer going down the road.

There's also this shock built in so that it . it's going to make sure that that air bag returns to its natural shape. And it's going to eliminate wear overtime from that air bag.This is going to have a scissor-like motion in the pin box, so it's going to compress and come back to normal. And that's going to compensate for that jarring and bouncing. And, again, that shock helps to keep that bag from breaking down over time.Now, by eliminating all that shock and jarring from the road, not only is that going to make your ride a lot more comfortable, but it's also going make sure that your truck and trailer last a lot longer if it's not having to deal with all that shock and trauma from the road going ...

while you're towing, it's going to make all those suspension components last a lot longer.And this is going to have a black powder coat that covers the entire thing, and that's going to prevent rust. It does have a sturdy steel construction and the king pin connects to any standard fifth wheel trailer. One thing to note with this is that it is not designed to work with any type of gooseneck adaptor, so keep that in mind.The bolt on installation is going to be really easy and there's no assembly required with this. It is, again, designed to replace the Lippert 1621 fifth wheel pin box. The weight capacity is 21,000 pounds.

And another thing to keep in mind with this is that is going to be very heavy. So whenever you install this, make sure you have a couple extra hands to get this on your fifth wheel trailer.That's going to do it for our look at the Trailair Flex Air fifth wheel Pin box.

Customer Reviews

Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs - LC369535

Average Customer Rating:  4.8 out of 5 stars   (4 Customer Reviews)

Flex Air drastically reduces chucking, absorbs road shock, and minimizes bounce. The internal air bag and built-in strut work with the rubberized pivoting head to achieve a dramatically smoother ride. Replaces Lippert 1621 pin boxes.

- LC369535

Formerly I had a hitch with air bags. Changed trucks with different mount. Looked to replace the easy ride and fell in love with this king pin. Now have several thousand miles and found this king pin better than the shock hitch! I would buy it again if something happened or we changed trailers!!!!!!!! I ordered the longer one and it allows me to let my tail gate down when hitched or hitching. Wonderful. 686918

- LC369535

product smooth's out ride over our great highways (cattle paths) here locally. only issue I have is that the pin box once tightened down into the original bolt holes is leaning to one side and is noticeable in the rear view mirror as I haul. 562437

has trouble keeping air in the 2 rubber doughnuts. seems that it needs top up a couple times a week when travelling. have heard that others have the same issues and have upgraded the rubber doughnuts to the 20K with better success.
Faith a - 09/09/2019


- LC369535

Great product for any fifth wheel! Really smoothes out the ride for both the truck and trailer. Easy bolt on install! All RVs should come with one of these! 572226

Best thing we ever did!
Unclefester - 10/07/2019


- LC369535

Great product with quick delivery. Does not come with mounting hardware, so if your existing pin box only bolts on with a couple of bolts you will more. Good idea to just order them at same time. Also did not come with glide (lube) plate as listed in info videos. 744543


Ask the Experts about this Lippert Components Fifth Wheel King Pin

  • Comparing the 18K and 21K Lippert 1621 Flex Air 5th Wheel Pin Boxes
    The Trailair Flex Air 5th Wheel Pin Box part # LC369535 which is rated for 21,000 lbs is constructed of a thicker metal and also has beefier welds when compared to the Trailair Flex Air 5th Wheel Pin Box part # LC328492 which is rated for 18,000 lbs. The air bag and shock that is used in each of them are the same. The thicker metal and welds are what gives the former a higher weight capacity. The best option for you would be the one that meets the GVWR of your trailer though you could go...
    view full answer...
  • Compatibility of Andersen 5th Wheel Ultimate Connection With Lippert Trail Air Air Ride Pin Box
    Thanks for the photo! I had Lippert run the serial number from the photo, and was told that you have a Lippert 1621 pin box. The compatible Trail Air Flex Air cushioned pin box is part # LC328492 for an 18K or # LC369535 for a 21K capacity. However, the Andersen Ultimate 5th Wheel Connection isn't compatible with the Flex Air without using a Rotaflex lock out kit, part # 3247 which is available from Andersen. Another alternative would be to use the standard Trail Air, which is # LC158778...
    view full answer...
  • How Important Is The Shock Line on the Trailair Flex Air 5th Wheel Pin Box
    I spoke to my contact at Lippert about the issue you are having with the Trailair Flex Air 5th Wheel Pin Box like part # LC369535 on your 2011 Ford F-350. They stated that the arrow on the shock is just a reference point and not something that you should really use as your absolute guide as they have had issues with the sticker being misplaced. The reason that the ride is so rough is that you are at near max psi of the airbag which is 120 psi. They recommend that you adjust the pressure...
    view full answer...
  • Trailair Flex Air Pin Box Recommendation to Replace 1621 Pin Box
    We have two Flex Air pin boxes that are a confirmed fit for replacing a Lippert 1621 pin box like what you have. We have the part # LC328492 which has an 18k capacity and the part # LC369535 which has a 21k capacity. This will work well with your 2017 Ram 2500 that has air autoleveling suspension. They would not fight each other or anything.
    view full answer...
  • Cushioned Pin Box Recommendation for 4200 Heartland Cyclone Fifth Wheel
    For your 4200 Heartland Cyclone the Trailair Flex Air part # LC369535 is the correct fit and would be the best way to smooth out the ride quality of your towing setup even further. This provides cushioning vertically and front to back so it's going to give you a smoother towing experience all around. It also has a 21k capacity which matches what you said you'd need as well.
    view full answer...
  • Comparing Trailair Flex Air 5th Wheel Pin Boxes For Lippert 1621 Pin Box Replacement
    The difference between the Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs # LC328492 and the Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs # LC369535 is only in the weight capacity. The air spring and shocks are the same on the unit designed for 21,000 lbs, so just the mounts on the trailer and the pin box itself is stronger. The Lippert 1621 pin box allows for either weight, so I recommend the one that is most compatible with the trailer GVWR. Either...
    view full answer...
  • How to Determine if a Flex Air Pin Box Will Clear Taller Bed Rails on a 2017 Ford F-350 Super Duty
    We haven't heard any reports of that specific combination having issues, but we do know that there have been issues with newer Ford trucks like your 2017 Ford F-350 Super Duty. The problem with clearance will not have to do with the Flex Air as much as it will have to do with your trailer. Basically you will want to make sure that you can adjust your pin box and 5th wheel hitch so that you have 5" - 6" of bed rail to trailer height clearance, and that the nearest point of your trailer...
    view full answer...
  • Flex Air or Air Ride Pin Box with Companion 5th Wheel Hitch
    One thing to ensure is that your Companion hitch is at the tallest height setting. This could provide an easy solution for connecting your king pin. I spoke to my contact at B&W, who confirmed that your Companion is compatible with both pin boxes. I also spoke with Trailair, who said that the Flex Air would provide you with over 6 inches in additional height. The Flex Air would also be the best option for eliminating chucking and creating a smoother ride. We offer the Flex Air pin...
    view full answer...
  • Upgraded Pin Box for a Grand Design Momentum 381M 5th Wheel
    Yes, the Trailair Flex Air 5th Wheel Pin Box part # LC369535 will replace the Lippert 1621 Pin Box on your Grand Design Momentum 381M. The Trailair Flex Air will provide a dramatic improvement in overall ride quality as well as reducing the amount of wear and tear on both the vehicle and trailer.
    view full answer...
  • Mounting Breakaway Switch to 5th Wheel Trailer Pin Box
    On 5th wheel pin boxes like the Trailair Flex Air # LC369535 that you referenced, the breakaway switch will typically be attached to the mounting brackets for the pin box. You will just want to find a secure surface on the trailer to mount the kit and battery box. This particular pin box is designed to replace the Lippert 1621 model pin box. It has a weight capacity of 21,000 pounds and features a pivoting head to cushion your ride and improve your handling. I have attached an article...
    view full answer...
  • Curt Q20 5th Wheel Hitch and Pin Box Compatibility
    The Curt Q20 Fifth Wheel Hitch # C16130 is compatible with a TrailAir cushioned pin box as well as other air ride pin boxes. What it is NOT compatible with are Sidewinder, Revolution or Turning Point pivoting pin boxes which move the truck/trailer pivot point from the hitch to the pin box, such as # RP61422.
    view full answer...
  • Cushioned Pin Box Recommendation for Toy Hauler with Lippert 1621HD Pin Box
    Since we know you have a Lippert 1621HD on your trailer we can easily pick you out a cushioned pin box. The Flex Air part # LC369535 will be what you need. It has a 21k capacity plus has two forms of cushioning for the pin box which will work great to smooth out your ride quality.
    view full answer...
  • New Decals for a Trailair L05
    Thanks for the photos. We do have the Replacement Decal for Lippert Components Trailair 5th Wheel Pin Box - GVW 21,000 # LC157285. We also have the Replacement Decal for Trailair 5th Wheel Long Style Pin Box - Driver's Side # LC157268. The warning decals we do not have available. I've not seen the bike rack mount in that location and it seems it would greatly reduce turning clearances so it must be for just storage when not in use.
    view full answer...
  • Can a FlexAir Pin Box be Used with an Andersen Ultimate 5th Wheel Connection
    Because the FlexAir pin boxes have a part that pivots it should not be used with the Anderson Ultimate 5th wheel connection. You can however use the Trailair equivalent which is # LC158778 for the Lippert 1621 pin boxes.
    view full answer...
  • Recommendation For Lippert Flex Air 5th Wheel Pin Box For 2014 Ram 3500 Crew Cab w/Long Bed
    I confirmed with Lippert that your pin box is a 1621 model so I recommend the Trailair Flex Air 5th Wheel Pin Box, Item # LC369535. The Flex Air will greatly reduce chucking, absorbs road shock, and minimizes bounce. It has a 21,000-lbs weight capacity and should serve you well. Contact me if you have any other questions.
    view full answer...
  • Recommended TrailAir FlexAir Pin Box Replacement for 2018 Forest River Silverback
    For your 2018 Forest River Silverback, the Trailair Flex Air 5th Wheel Pin Box # LC369535 is the correct fit. It will work with the capacity of your trailer as well as will bolt right up to your 1621HD pin box. The only real difference between the 1621 and 1621HD is the HD uses thicker material but has the same dimensions.
    view full answer...
  • How Much Does the Trailair Flex Air and Rota-Flex Pin Boxes Weigh
    The Trailair Flex Air 5th Wheel Pin Box part # LC369535 weighs around 230 lbs and the Trailair Rota-Flex 5th Wheel Pin Box part # LC328330 weighs around 100 lbs. They are both designed to replace a Lippert 1621 pin box.
    view full answer...
  • Cushioned Pin Box Recommendation for 2017 Forest River Silverback 33ik
    I looked up the weight of your 2017 Forest River Silverback 33ik and it looks to be right at 14k so the 18k Flex Air part # LC369535 that you referenced would work well. I appreciate you listing that you have a 1621 pin box too as that makes picking out the correct replacement much easier.
    view full answer...
  • Could TrailAir Flexair Pin Box Replace Mor/Ryde Pin Box
    As long as the Mor Ryde pin box you have was designed to replace a 1621 Lippert pin box the Trailair Flex Air pin box part # LC369535 would fit and work well. Most likely your MorRyde would have a part number like Mor/Ryde SPB72-1621LD which if so you can see the "1621" in the number which means the Flexair mentioned is the correct one.
    view full answer...
  • Should I Deflate The Air Bag Of The TrailAir Pin Box When It's in Storage
    If you did leave air in the bag of the Trailair pin box like part # LC369535 it wouldn't be a big deal however, we do recommend to deflate the bag to keep the pressure off the bag and fittings while it's in storage. You definitely want to cover the pin box to avoid UV ray damage that causes dry rot of the rubber.
    view full answer...
  • Troubleshooting Trailair Air Ride Pin Box Not Holding Air To Line on Shock Sticker
    The Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs # LC369535 will have an air bag pressure range between 20 and 120 psi. Lippert techs say that sticker is there to assist but is not always accurate due to the fact it is a sticker that can be slightly misplaced. If your air bag is within the 70-100 psi range then they said not to worry about the sticker. It is a reference point and not a perfect guide. I recommend using a pressure gauge to confirm the 70-100 psi as...
    view full answer...
  • Which Trailair FlexAir Fits Trailer w Lippert 1621 Pin Box and Capture Plate to Use with Pullrite
    While we don't carry Pullrite hitches we have found in the past that the capture plate part number for using a FlexAir pin box should be part number PR_331756 or PR_331760. You'd want to check with them to verify this. The FlexAir part number # LC369535 is the correct fit for your trailer that has a Lippert 1621 pin box installed currently.
    view full answer...
  • Best Cushioned Pin Box Recommendation for 2019 Columbus by Palomino
    Your 2019 Columbus by Palomino does have a Lippert 1621HD pin box on it so the best cushioned pin box replacement available is the Flex Air part # LC369535. This offers vertical and horizontal cushioning and has a 21k capacity so it will give you the ultimate ride quality improvement from a pin box.
    view full answer...
  • 5th Wheel Towing with 2018 Ram Mega Cab with Short Box
    Lippert's Trailair Flex Air 5th Wheel Pin Box # LC369535 that you referenced is designed specifically as a bolt on replacement for their OEM model 1621 pin box. It appears you have a different model of telescoping pin box. The Flex Air will not work. 6-1/2-foot bed trucks need a sliding 5th wheel hitch which usually give you 10 to 12-inches of travel for extra turning clearance. Some hitches like the 18K Demco # DM8550034 and the 21K Demco # DM8550035 give a full 14-inches of travel...
    view full answer...
  • Is There Capture Plate Available From PullRite to Fit Trailair Flex Air Pin Box
    We do not sell the capture plate you need but it is 331761. That is the model indicated by PullRite that fits the Flex Air pin boxes such as # LC369535.
    view full answer...
  • Does Air Pressure in Trailair Flex Air Pin Box Need to be Deflated at Any Point
    There's no inflation/deflation maintenance schedule for the air bags in the Trailair Flex Air pin boxes like the # LC369535 that you referenced. Whatever PSI rating your towing setup requires can be left in at all times. Air bags are not known for wearing out either. If they were we'd see that question come up as there are so many of these on the road and we sell a lot as well. People requesting replacement bags is basically unheard of. I'd be shocked if you ever ran it to needing a new bag.
    view full answer...

Do you have a question about this Fifth Wheel King Pin?

  • Why etrailer.com?

    At etrailer.com we guarantee:
  • Highest quality fifth wheel king pin for the best price.

    Our Lowest Price Pledge ensures you will never overpay for the parts you need.
  • Real product know-how.

    We make sure that the products we sell are what we say they are, and that they work the way they are supposed to work. Get real advice from a real person who has the knowledge and expertise needed to solve your problem.
  • Most detailed, accurate fifth wheel king pin information available.

    Because we take providing accurate product information seriously, we take our own detailed product photos, demo videos and installation videos, as well as verify measurements, instructions, and vehicle fit information.
  • Installations, made easy.

    We love helping people and have the most highly-trained customer service, hands-on experience, step by step videos and installation instructions.
  • Fast shipping.

    Your order is automatically routed to get out of our warehouse and to your door as quickly as possible. Receive free shipping on orders over $99.
  • Personalized service for life.

    We provide one-on-one, personalized service from the ordering process through the life of your product.
  • Trusted since 1946.

    We've been serving customers since our parts store first opened in 1946 and continue to be recognized by our customers, our vendors and third parties for exceptional service.
  • Returns Policy

    Need to return an item? No problem. Please read our Returns Policy for more information.

Info for this part was:

Expert Research:
Mike L
Expert Research:
Michael H
Expert Research:
Jameson C
Expert Research:
Adam R
Edited by:
Lindsey S
Installed by:
Kathleen M
Written by:
Shelly K
Updated by:
Hannah L
Updated by:
Kristina F
Updated by:
Matthew E
Updated by:
Isabelle B

At etrailer.com we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time. Let us know if anything is missing or if you have any questions.