How To Find Out What Pin Box You Currently Have To Determine A Correct Replacement
Updated 02/11/2026 | Published 12/28/2021
Question:
Looking to replace the stock pin box on my 2020 cyclone 4006 with the flex air and want to make sure I get the right model.
asked by: Matt L
Expert Reply:
The Trailair Flex Air 5th Wheel Pin Box # LC369535 you mention will replace Lippert 1621 pin boxes, so if you have a 1621 pin box this will work for you. If you are unsure which pin box you currently have, you should be able to locate the manufacturers name, along with the model number printed on a sticker usually on the pin box itself.
If you aren't able to locate any sticker information, then you're going to need to make a couple of measurements. You'll need to measure the horizontal bolt 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.
Once those measurements are made, you can find out what pin box you have using the chart located in the FAQ attached to this answer page.
(click to enlarge)
(click to enlarge)
(click to enlarge)
(click to enlarge)
(click to enlarge)
Product Page this Question was Asked From
Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs
- 5th Wheel Pin Box
- Upgraded Pin Box
- Absorbs Road Shock and Reduces Chucking
- 21000 lbs
- Air Ride Suspension
- Fixed Turret
- Lippert 1621
- CURT
more information >
Featured Help Information
Miscellaneous Media
Continue Researching
- Search Results: 5th wheel gooseneck adapter
- Search Results: gooseneck hitch
- Search Results: fifth wheel hitch
- Search Results: 5th wheel trailer to gooseneck hitch 5th wheel gooseneck adapter
- Q&A: Is There a Gen-Y Nomad Gooseneck Pin Box Available to Replace a Rhino-Box?
- Shop: Shocker 5th Wheel to Gooseneck Pinbox for Lippert 1621/0719 and Rhino Box - 24K GTW - 6K TW
- Shop: Gen-Y Hitch Nomad 5th Wheel to Gooseneck Pin Box - Lippert Rhino - 30K GTW - 6.5K TW
- Article: 4 Steps to Choosing Your 5th Wheel Pin Box
- Shop: Curt Helux 5th Wheel to Gooseneck Shock-Absorbing Pin Box Adapter - 20K GTW - 5,000 lbs TW
- Shop: Gen-Y Hitch Shock Absorbing 5th Wheel to Gooseneck Pin Box - Lippert Rhino - 24K GTW - 4.5K TW
- Shop: Curt Helux 5th Wheel to Gooseneck Shock-Absorbing Pin Box Adapter - 20K GTW - 4,300 lbs TW
- Q&A: Fifth Wheel to Gooseneck Adapter to Replace Lippert 1621 Pin Box
- Shop: Curt Rota-Flex 5th Wheel Pin Box - Lippert 1621 - 21,000 lbs
- Shop: Safety Chain with 2 Hooks for Gen-Y 5th Wheel to Gooseneck Pin Box - 84" Long - 26,000 lbs
- Q&A: What Is An OEM Prep Package And How Do I Know If I Have It
- Search Results: trailer hitch
- Shop: Trailer Wiring
- Q&A: Does Truck with 6-1/2 ft bed Have to Use Slider Hitch for Turning Clearance with Fifth Wheel Hitch
- Article: Trailer Wiring Diagrams
- Video: Firestone Ride-Rite Air Bags with Easy Mount Compressor Feature Breakdown
- Search Results: trailer tires and wheels
- Q&A: Installation Time for Blue Ox BX1128 Flat Tow Base Plate Kit for 2016 Jeep Grand Cherokee
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Video: B&W Companion OEM 5th Wheel Hitch Manufacturer Breakdown
- Article: Gooseneck to 5th Wheel Adapters
- Q&A: What is the Difference Between a Class II and a Class III Hitch?
- Video: In-Depth Look at the B&W 5th Wheel to Gooseneck Pin Box
- Shop: Brake Controller
- Video: Smoother Towing Solution: Gen-Y Hitch Nomad 5th Wheel to Gooseneck Pin Box
- Search Results: trailer wiring
on 5th Wheel Pin Box
Sven M.
2/11/2026
Looking to replace the same pin box. My reason (other than comfort) is that I need a bigger gap in between the trailer and the truck bed. We have 1 spot on the driveway where the long bed truck bed hits the trailer. And we camp off road and sometimes the uneven dirt causes the truck to hit the trailer. I need 1 more inch of gap in between th truck bed and the 5th wheel. I’m maxed out on the pin box and on my BW Companion hitch. Will I get more adjustment on a different pin box?