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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
Mike L.
4/7/2026
Glad we could help you out, Lowell!
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.
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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 :)