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This Rota-Flex pin box has a pivoting head with a built-in rubber compound that works to reduce chucking and absorb road shock, resulting in a smoother ride and less wear and tear on your trailer. Replaces Lippert 1621 or 1621HD pin boxes.
Features:
Specs:
Notes:
The Rota-Flex pin box has a pivoting head and built-in rubber compound that help to reduce chucking and absorb road shock for a smoother ride as you tow your fifth-wheel trailer.
The pivoting head on the Rota-Flex 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 Rota-Flex 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.
A heavy-duty rubber compound is built into the head assembly of the Rota-Flex pin box. This rubber absorbs the bumps and vibrations, or road shock, 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 Rota-Flex takes the beating so there's less wear and tear on your trailer or RV and you get a smoother ride.
Easy, Bolt-On Installation
The Rota-Flex is easy to install. Simply remove your existing Lippert 1621 or 1621HD pin box and install the Rota-Flex on your trailer or RV. The Rota-Flex uses the same bolts that held on your original pin box so no additional hardware is required. Plus, it comes out of the box ready to be put on your trailer, so no assembly is needed. Because the Rota-Flex is quite heavy, you should put it on an elevated surface or have a friend help you support its weight during installation.
Customer Satisfaction Score:
94% were satisfied with this product
6% of customers were not satisfied
Ratings & Reviews
Worked fine, easy to install only used for one trip to Michigan and sold trailer.
Fast shipping and item fits perfectly. Replaced old pin box by myself with a small tractor in about 45 minutes. Can't wait to try it out on my new toy hauler.
I've had this pin box on other fifth wheel trailers with great experience.
Great customer service and timely shipping.
Product was as expected.
It got lost by UPS, but the service and customer service was great, received my product in excellent shape. This is a very good company to do business with. I will do business with them again. Thank you Paul.
I purchased it as a direct replacement for the damaged on on my fifth wheel.
The difference now compared to when I had my done is like night and day, no more chucking, very little if any jarring , the ride meets al my expectations
Perfect fit for the Lippert 1621/1621HD pin box. The only issue is with most big parts I order from Etrailer is the packaging is extremely poor as this box like others was torn completely open. Do to the continual packaging issues I give them a 3. The hitch gets a 5.
I received my order promptly, faster than expected for a large item. I paid for my pin box, checked the next day and etrailer had dropped the price, they refunded the difference which impressed me greatly. I am a repeat customer and have not had a bad experience ever.
Received the Roto flex pin box I ordered from etrailer in about a week. Arrived in good condition and perfect fit completely satisfied with etrailer on this order
The Trailair Rota-Flex pin box worked great. The pin box did the job by removing 80% of the chucking as we traveled.
Came in mail packaged! Even the UPS man told me how etrailer is a legit company doing a great job shipping! Any in costumer service was great and her team had the price match over amazon done in one business day. Great to work with!!
Had trouble receiving the hitch through UPS (they lost it --[48 miles from my residence] conversation with Stacy at etrailer and they shipped another, which my wife and I installed. etrailer was very helpful in sending another to replace the one UPS lost. Thanks so much
The Trailair Roto-Flex is an excellent product. It really has smoothed out the ride and handling of my fifth wheel, especially over roads that aren't so perfect. I highly recommend this for an upgrade.
This king pin assembly works well to get the chucking down. I do feel at times do to road conditions that I still feel some, but over all it has helped the ride and I feel it has take some abuse away from my truck and the trailer seems to ride better. Overall I am pleased with the kingpin assembly for the cost. The only thing I cannot do is put my cover on that was on my old kingpin.
No bucking and jerking has made for enjoyable RV experience this year. One of the best investments I've made in our RV. prompt handling and shipping from etrailer made it even better!
Looks great on my 5th. If anyone else has wondered as I did and could not find anything online regarding the vertical height difference between this trail air rota flex and my standard lippert 1621. This pin box will reduce the nose of my 5th by 2" mounted in the same location. Now to pull my rear axle spacers on my dodge to get another 1.5" lower. Etrailer is great as always. Never had a problem with them and have ordered here many times. Thanks Etrailer!
Fast Shipping,Great product,It sure softens up the ride! Doesn't eliminate all the jerking but overall quite satisfied! Quality built product. Definitely not a one person job so seek out a helper to hold things Thanks Etrailer.
Great product fit like a glove
Joanne at e tráiler was very knowledgeable and helpful. The shipping was fast and best of all free. Seems like a great company. I will install the new pin box in a day or so then going on a short trip to give it the test.
The product was great, The better part was how fast it got to me . I had it put on the camper the same day i had received it what was 3 days after my order. Now you can't beat the shipping. All my orders from ETrailer has been fast and on time . Thank you all at Etrailer.
Received on Wed. as planned. With a little help from my forklift, I had this trail air pin box installed in few hours. Fit perfect on my Sabre. Drove around the block, about 4 miles. This pulls so nice, it is like nothing behind you. Thanks etrailer.
I received the RotaFlex on date that was scheduled although box was tore open all items were in box It would be great if mounting hardware and torque values were included I had to call trailer and ask for that information Everything went together perfectly
I have other on other trailers is why I purchased this one. Improves ride.
Hannah did an excellent job of working with me to find the correct upgrades for my towing system. 5 stars got her. Tge package arrived with the king pin poking through the box and having deep scratches. I think it will function ok. 3 stars for those handling shipments and deliveries.
Brooke M.
3/18/2025
Let us know if any of the damage goes further than just cosmetic! Thank you for the kind words about Hannah, too! Ill make sure she sees your review :)
Mark
3/15/2026
The Curt 5th wheel king box I received from Etrailer a year ago has worked very well. Trips to CO elk hunting and ND duck hunting have been problem free. The Curt pin box coupled with my B & W 16,000 lb Patriot 5th wheel hitch have provided a very smooth and reliable towing experience for my 7,000 lb 5th wheel pulled by my 2024 GMC Sierra 1500 short box. The customer service at Etrailer is the best in the business, IMO, and the demo videos are super helpful.
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Gene
10/19/2013
This king pin box came on my 5th wheel, it does not help the jerking at all. I am now looking to install a different pin box.