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Keeping the axle tight to the leaf springs is what keeps your trailer tracking true. This U-bolt kit uses Grade 5 hardware for dependable clamping strength on 3,500-lb round axles with a 2-3/8" diameter. Each U-bolt is 5-1/2" long and 7/16" in diameter, giving plenty of thread engagement for a secure hold that stays tight mile after mile.
No guessing which parts go together—this kit includes four U-bolts, two plates for 1-3/4" wide springs, and eight 7/16"-20 hex nuts. Spring seats are required for mounting but sold separately, so you can choose the right setup for your suspension. Everything fits cleanly and lines up like it should for a solid connection.
Proper torque means no shifting or loosened hardware down the road. These U-bolts are designed for a torque range between 45 ft-lbs and 70 ft-lbs, giving you a clear spec to follow during installation. It’s the reassurance that once tightened, your axle and springs will stay locked together through bumps, turns, and long hauls.
Each steel part comes with a light oil coating to help inhibit corrosion during storage and early use. It’s a practical finish that keeps rust at bay before you get your trailer back on the road or trail. When you need a straightforward, heavy-duty way to mount your axle, this kit just works.
Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Speaker 1: Today we're going to be taking a look at the Redline U-bolt kit for mounting 3500 pound round trailer axles. These are 5 1/2 inch long U-bolts. The part number is APUBR-1.Now, when replacing your axle, it's a really good idea to also replace the U-bolts. These are a pretty cost effective item you can get and ensure that you're going to have excellent, excellent hold with your axle to your springs. You can see this is going on a floor spring pack. The opening on them is going to be 2 3/8 inch, so it's going to fit the outer tube diameter of our axle here.
It comes with the new lower plate, and also four new flange nuts that allows you to secure that end, keep everything locked tight, so you don't have any issues for a very long time.Now we're going to remove the four nuts on the bottom here that hold our axle down, and they hold the U-bolts here. When replacing an axle, generally you're going to replace these as well, just because these can kind of stretch over time. So, if these nuts won't come off, you can also just cut your U-bolts on each side.Now we're going to grab our new U-bolt kit and place these down and around, just like our old U-bolts were, and when we we'll replace the bottom bracket up on the U-bolts we'll see the hole here in the middle. That's meant for that nut to come down through, and then in each position we'll install one of the flange nuts.Now we'll go through and you're evenly going to tighten down our bolt. We'll get them snugged up first and then we can torque them.
For these nuts you'll want to use a 19 millimeter 3/4 inch socket. Notice we're tightening them evenly, but in a crossing pattern.That's going to compete our look at the U-bolt mounting kit for 3500 pound round trailer axles, part number APUBR-1.
Customer Satisfaction Score:
94% were satisfied with this product
6% of customers were not satisfied
Ratings & Reviews
Just as advertised. Quality parts.
Last project built. Used etrailer for almost all parts, 7 pin wiring harnesses, junction block, tail lights, jacks, spring retainer bolts vent cover and so on. Love the leveling jacks. Friend wants one now so started another one. I will be getting all the parts from etrailer...
Fit perfectly for my trailer. All the components seem to be heavy duty.
Awesome job
They fit perfectly and were a high qual ity
Exact fit for my 3500 lb axle.
Products fit as expected
When the U bolt kit arrived it was inside another box with leaf springs. 2 of the nuts for the u bolts were missing causing me to stop the project and go to the hardware store.
One of the wet bolts wouldn’t take grease and required a LOT of extra time and hassle to get it working…just short of contacting you folks with a defective part complaint… we were finally able to get it functioning.
Other than that, it was a straight forward ( much needed) rehab of a 17 yr old, 16’ flatbed trailer that is routinely used to haul tons of hay, farm equipment and building materials.
Great to have ‘kits’ organized to get this project done. Made ordering quick and delivery was fast. Thanks.
replaced my old axle and hubs with a heavy duty axle, U-bolts and new hubs. It has all held up well. I had to custom weld the axle carrier to fit my trailer, but everything fit well, and was a fairly easy installation. I now feel much more confident with a 3500 lb. axle and these heavy duty U bolts under my trailer.
Product installed perfect and has lasted many miles of use without any problems
Metric, plain nuts, no locknuts, no lock washers.
I recently replaced my 1/2 ton truck with a 3/4 ton truck. In order to hook up to my existing fifth wheel camper, I had to raise my camper. To do this, my brother and I moved the axles from the top of the leaf springs and attached them under the springs. This kit made it very easy to do this. We torched off the old u bolts and used this set as a replacement. The quality of this kit was very good. Hard to get too excited about u bolts but I would purchase this again if I had to do it all over again.
I was able to gain about 5 1/2 inches by flipping the axles. Here is a before and after.
Always a pleasure dealing with etrailer. Great stock of parts and very knowledgeable.
Perfect replacement for stock hangar
After I finally got the right set,(totally my fault, I didn't measure correctly). These were the perfect pick. Neil was a great guy helping me with all the returns and the correct ones. Great company, great customer service!
Fit perfectly easy change out great customer service
Mike L.
4/7/2026
Glad we could help you out, Lowell!
Awesome product as well as even better service from Eli and everyone who has helped me with my suspension project
Fit perfect, trimmed extra thread off after completing installation
Well out of the order we are missing the bearings we are missing to hubs/rotors we are missing the break lines we are missing the seals we are missing half of a shackle all while the trailer is sitting in my garage taking up space I called in already now I have to call back as I just realized about the hubs plus I can’t upload the photos PLEASE HELP GET ME THIS STUFF.. thanks
These made installation of the new springs much easier and safer.
Expensive for these bolts. Seems like they should be half the price. Had to use my own washers.
Good quality definitely recommend using this kit when replacing old leaf springs as the old one get tired and threads can get worn out and stripped when taking the old pair off to do repairs.
New suspension parts made a real difference in trailer handling. Original shackles holes were severely elongated, spring eye mounts were also needing attention. Thank you, etrailer for the needed parts and support.
Victoria H.
4/3/2025
Sounds like your trailer suspension got a full rejuvenation Roy! Now you can keep hauling with confidence and we'll be here if you need anything else along the way :)
Great product unfortunately I had to return the u bolts. Cause our trailer, unbeknownst to us the axle were undated to 5,000 pound axles. They sent me replacements, and I got return labels to ship them back at no cost to me. I highly recommend e trailer to anyone needing trailer parts.
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Sgtbass64
12/9/2016
Well, its been a year and I am still very impressed with the suspension parts I got from eTrailer. I have ran my car trailer from Michigan down to southern Ohio, Indiana, and Illinois. Had no issues what so ever. The trailer handled beautifully.