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  1. 5th Wheel Pin Box
  2. CURT
  3. Lippert 1621
  4. 21000 lbs GTW
  5. Upgraded Pin Box
  6. Absorbs Road Shock and Reduces Chucking
Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs
CURT

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

Part Number: LC369535
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$1,676.50
Retail:$2,062.95
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5th Wheel Pin Box
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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. 1-800-940-8924 to order CURT 5th wheel pin box part number LC369535 or order online at etrailer.com. Free expert support on all CURT products. Great prices and Fastest Shipping for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs. 5th Wheel Pin Box reviews from real customers.
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CURT 5th Wheel Pin Box - LC369535

  • Lippert 1621
  • 21000 lbs GTW
  • Upgraded Pin Box
  • CURT
  • Absorbs Road Shock and Reduces Chucking
  • 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.


Features:

  • 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


Specs:

  • Designed to replace Lippert 1621 5th-wheel pin box
  • Weight capacity: 21,000 lbs
  • Overall width: 12"
  • 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"
  • Distance from center of king pin to front row of bolt holes: 20-3/4"
  • Distance from center of king pin to back row of bolt holes: 28-5/8"
  • 1-Year limited warranty


Notes:

  • Do not use the Curt Flex Air pin box with any type of gooseneck adapter.

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 Curt 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

Curt 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.


Curt 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

Curt 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 Curt Flexair Fifth Wheel Kingpin Box for Lippert 1621 - 21,000 lbs

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




California residents: click here


Customer Satisfaction Score:

Ratings & Reviews

4.5

184 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.

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See what our Experts say about this CURT 5th Wheel Pin Box

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  • Replacing/Upgrading Pin Box On A 2018 Grand Design Solitude
    Hello Micael. I can definitely help point you in the right direction. An Air Ride Pin Box like the Curt # LC369535 will definitely be an upgrade from a standard pin box. What is the bed length of your truck? If you have a long bed, clearance will not be an issue. Short bed trucks are where you can run into potential clearance issues. Some short bed trucks may require the use of a sliding fifth wheel hitch. If you have clearance with the current pin box, you should be good though. As...
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  • Compatibility of Curt Air Ride and Flex Air With Andersen 5th Wheel Hitch
    Hello again Joel; I would recommend the Curt Air Ride 5th Wheel Pin Box # LC158778 over the Flex Air # LC369535. The pivoting head from the Flex Air causes too much movement so it actually isn't compatible with the Andersen hitch. Since the Air Ride is just a cushioned pin box it can be used with the Andersen. The Air Ride weighs 184 lbs and the Flex Air is 232 lbs. With the updated information from below I recommend the MORryde Cushioned 5th Wheel Pin Box # MR37VR. This fits a 1716 bolt...
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  • Best Pin Box Upgrade Recommendation for 2017 Grand Design Momentum with a 1621 Pin Box
    For your 2017 Grand Design Momentum that has a Lippert 1621 pin box the best upgrade we have is the Trailair Flexair part # LC328492. This has cushioning vertically and a pivoting king pin plate that allows for cushioning front to back as well. This will give you a noticeable smoother ride quality than what you currently have.
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  • Recommended Pin Box an Suspension Upgrade for a 2025 Venture Sporttrek 353VIK 37’ 5th Wheel
    Hey Tom, congrats on the new 5th wheel trailer and thank you so much for all of the information! I recommend the Gen-Y Hitch Shock Absorbing 5th Wheel Pin Box item # GY68GR. The Gen-Y has a rubber torsion spring design that helps absorb both downward and upward movements from the trailer when hitting a bump in the road. Other shock absorbing pin boxes, like the Curt Flex Air item # LC369535, use an air spring and shock that are great for downwards forces but aren't the best at pulling...
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  • Lippert 1621 SHD Replacement and Compatibility With B&W 5th Wheel Hitches
    The Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000lbs Item # LC369535 is a compatible replacement for your current 1621 SHD pin box. B&W hitches have a rounded 2-piece jaw on this fifth-wheel trailer hitch inhibits rattle and movement by securely wrapping around your trailer's king pin, so you shouldn't have any issues coupling your new pin box.
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  • Determining The Correct Flex Air Pin Box For A Grand Design Solitude 391DL 5th Wheel Trailer
    To determine which Flex Air pin box will fit your Grand Design Solitude 391DL you'll need to first determine your pin box bolt pattern. There will typically be a sticker somewhere on the pin box or mounting ears that has a serial number, RPO number, and LCI item number on it (pictured below) that we can use to determine the pattern. If not then you'll need to use the attached help article below to measure for your bolt pattern. For example, the Curt Flex Air 5th Wheel Pin Box # LC369535...
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  • Will The Curt Flex Air Pin Box Add More Clearance Than The Rota-Flex Pin Box
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  • How Much Does the Gen-Y Shock Absorbing 5th Wheel Pin Box Weigh
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  • Trailair Flex Air Pin Box Clearance From Tailgate And Bed Rails Of A 2017 Chevy Silverado 2500
    The Trailair Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000lbs # LC369535 has 3" difference from king pin to front bolt row when compared to a standard 1621 pin box so it will be that much closer to your tailgate and sides. This will slightly help with turning clearance and the height difference can be adjusted if your 5th wheel hitch has an adjustable hitch head. I recommend hooking up to your trailer and measuring from the distances you currently have to see if you can accommodate...
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  • Comparison of Curt LC158778 and Curt LC369535 Flex Air Pin Box for Lippert 1621HD
    Both the Curt # LC158778 and the Curt Flex Air # LC369535 would be compatible with both the Lippert 1621 and 1621 HD OEM pin boxes, as both share the same mounting bolt pattern. The only difference is the higher capacity of the HD model. Both pin boxes will do a great job of isolating the tow vehicle from much of the bouncing, shock and chucking experienced by the 5th wheel, but the # LC369535 Flex Air goes a step further with a dampened pivoting head that helps limit lateral movement or...
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  • What is the Difference Between the Trailair Air Ride and Flex Air for a Lippert 1621 Pin Box
    Even though both the Trailair Air Ride # LC158778 and the Trailair Flex Air # LC369535 look similar and incorporate the air bag and shock to help improve your towing experience, the Flex Air has a few upgrades that the Air Ride does not have. The 2 things that separate these 2 5th wheel pin boxes is that the Flex Air has a rubber compound that is built into the head assembly which really helps to absorb road shock. The Flex Air also has a pivoting head which gives you controlled back and...
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  • 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...


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Used Items Available
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs

Condition: Surface Scratches

Notes: Item has cosmetic scratches and scrapes. Otherwise new and unused.

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