1. Fifth Wheel King Pin
  2. Lippert Components
  3. Lippert
  4. 1621
  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
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Fifth Wheel King Pin
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Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs Lippert LC369535
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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.
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Lippert Components Fifth Wheel King Pin - LC369535

  • Lippert
  • 1621
  • 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

Customer Reviews

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

Average Customer Rating:  4.8 out of 5 stars   (11 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

Absolutely Wonderful! After a year and over 10,000 miles I could not be happier with this hitch. Easy to hook up and unhook with safety features that allow you to easily see it is hooked properly. Over the past 25 years I have purchased 3 5th wheel hitches and by far this is the top of the line without the top of the line price. Several people have ordered because of seeing our hitch.
Dennis P - 08/14/2020


- 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

Christina was wonderful - walking me through issues involved with the purchase, and following up throughout the process all the way up to arrival at my door. 5-star customer service by her and Etrailer! 918725

- LC369535

Really nice piece, install was a breeze other than it being really heavy! It definitely improved the ride of my 45 foot toy hauler but it also raised the front of my unit about 3 inches (with the airbag inflated to 90 psi) and that’s after I lowered my hitch to its lowest setting. 900559

- LC369535

Believe the hype! This kingpin is the “kingpin of kingpins”. I went from my straight 1621 to this. The difference was astounding. It was like going from being on the SS Minnow on rough seas to the USS Nimitz on a calm bay. Very little chucking. True night and day difference. Yes, it is a little pricey, but if you consider the potential outlay of cash to the incurred maintenance of wear and tear from travel to BOTH the tow vehicle and trailer-I felt it was worth the investment. If you’re looking into upgrading-do it. It’s worth it! 821941

- LC369535

Great product. No problems after one year. Helps a lot with the bucking on rough roads. Highly recommend. 818369

- LC369535

The reason I purchased the pin box is I needed some extra distance between my truck bed and 5th wheel. It did the trick, I got an extra 5" (had 4"). But the ride is amazing! Very pleased with towing, I almost can't tell I'm pulling a 44' toy hauler cause it's so smooth. My ordering experience was top notch, I will definitely purchase again from etrailer.com 814909

- LC369535

Smooth out the right of the fifth wheel so well reduce chucking I will never buy another fifth wheel without this hitch 765074

- LC369535

This is an awesome upgrade it takes the chucking away 100% smoother than the standard king pin, the only issue is that after setting at one location for awhile I have to top off the air? It is definitely a great addition to the HL Landmark 765030

- LC369535

The hitch pin box did exactly what I wanted it to do. It gave me more bed clearance and a better ride for the fifth wheel. The only drawback, is that it touches the side of the bed on sharp turns. 764392

- 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

- 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


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...
  • 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...
  • Trail Air Flex Air Replacement for Lippert 1621 OEM 5th Wheel Pin Box
    The pin box shown in the photo you provided (thanks for that, by the way!) does indeed show a Lippert 1621 OEM pin box. The Lippert # LC369535 Flex Air you'd looked at is the correct replacement for a Lippert 1621 OEM pin box. However, since your OEM pin box only has a 15.5K capacity, there's really no reason to spend more for the 21K version. I'd recommend saving a few bucks and going with the 18K version, part # LC328492 which would still work perfectly for you. I've linked to a...
    view full answer...
  • How To Improve Ride Quality With Andersen Ultimate Connection Gooseneck
    I may have an option for you but the Trailair Flex Air 5th Wheel Pin Box for Lippert 1621 part # LC369535 is not compatible with an goose neck adapters including the Andersen because it puts too much stress on the ball. I recommend to use the 5th Airborne Premium Fifth Wheel Air Ride Coupler part # 5AB-E1621-610 which is a cushioned replacement for the Lippert 1621 pin box. The coupler acts as a buffer between the tow vehicle and trailer to minimize road shock. I have attached an installation...
    view full answer...
  • Correct Capture Plates to Use FlexAir Pin Box with Demco Hijacker Autoslide
    Yes. You can use the Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs # LC369535 with the Demco 21K Hijacker Autoslide 5th wheel hitch for 2016 Ford OEM Prep Package # DM8550038 when you use the Demco Hijacker Autoslide Capture Plates for Trailair Rota-Flex Pin Boxes # DM6171. If you've got a Demco Hijacker that isn't designed to fit in the OEM prep package, you can use the Demco 5th Wheel Rail Adapter for Ford OEM 5th Wheel Towing Prep Package - 25,000 lbs # DM6175 to...
    view full answer...
  • Difference Between the Lippert Flex Air and Air Ride Pin Boxes
    The difference between the Trailair Flex Air # LC369535 and the Trailair Air Ride # LC158778 is that the Flex Air has a pivoting head that is designed to help reduce chucking. Aside from that they both have the air bag and the shock to help improve ride quality. Attached are some review videos that you can check out.
    view full answer...
  • Will the Trailair Flex Air 21K Pin Box for Lippert 1621 Work On an 18K GVWR Trailer
    Yes, the Trailair Flex Air 5th Wheel Pin Box part # LC369535 which is rated for 21,000 lbs will work just fine on a trailer with Lippert 1621 Pin Box and 18,000 lb gross vehicle weight rating (GVWR). The gross vehicle weight rating is the most the trailer can weigh fully loaded so you will never exceed the weight capacity of the pin box and even have a few thousand lbs of wiggle room.
    view full answer...
  • Is Trailair Flex Air Compatible With B&W Companion Slider on 2018 Ford F-350 With Puck System
    The Trailair Flex Air 5th Wheel Pin Box # LC369535 is absolutely compatible with the B&W Companion OEM 5th Wheel Trailer Hitch with Slider for Ford Towing Prep Package # BWRVK3370. The Companion slider is not compatible with pin boxes that change the pivot point of the king pin - rotating pin boxes - but is compatible with cushioned pin boxes that provide a better ride. The Flex Air is also going to provide benefit to you even though your 2018 F-350 has the Firestone Ride-Rite Red Label...
    view full answer...
  • How To Determine If The Trailer Will Be Level After Installing the Trailair Flex Air Pin Box
    The Trailair Flex Air 5th Wheel Pin Box part # LC369535 is an excellent option for an upgraded pin. In regards to dimensions, these will be similar to the pin box it replaces as the pin boxes that fit this bolt pattern are all relatively the same dimensions. If you have concerns of towing level then there are adjustments you can make to both the hitch and pin box. In order to be certain you will be level once everything is installed, it would be a good idea to measure this before hand....
    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...
  • What is Recommended Torque for Pivot Bolt of Trailair Pin Box King Pin Plate
    I checked with our contacts at Trailair and the correct torque figure for the pivot bolt of your Trailair pin box is 50 ft lbs.
    view full answer...
  • Using Air Ride 5th Wheel Hitch Together With Air Ride Pin Box
    I've seen the Trailer Saver before, it looks like a great hitch but we don't have any personal experience with it. I've done some research though, and I can certainly see how a flexible linkage between the hitch and vehicle (air bags on the hitch) and a flexible linkage between the king pin and the fifth wheel (air bag in the pin box) could tend to amplify the chucking. I did some searching around, and really the only online opinions I can find pretty much mirror what Trailer Saver's...
    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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • Air Ride Pinbox Compatible With a Steelco/Davis Pin Box PB02 or PB02W?
    There is not a Flex Air pin box fit for your Steelco/Davis PB02 or PB02W pin box. There is similar option available in the Trailair Air Ride 5th Wheel King Pin - Steelco/Davis, Venture - 21,000 lbs # UF35-946211 that is a fit. You won't have the additional pivot with cushioning at that pivot found in the Flex Air, but you will still have the air ride adjustable replacement for your current pin box.
    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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...

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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:
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Updated by:
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Updated by:
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