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  1. Trailer Leaf Spring Suspension
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  3. U-Bolt Kits
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  5. Round Axle - 2-3/8 Inch
  6. 5-1/2 Inch Long
U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts

U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts

Item # APUBR-1
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Trailer Leaf Spring Suspension
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Redline Axle Mounting Hardware - APUBR-1
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Mount your round, 2-3/8" diameter axle to your trailer's leaf springs with this U-bolt kit. U-bolts, plates and nuts included. Lowest Prices for the best trailer leaf spring suspension from Redline. U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts part number APUBR-1 can be ordered online at or call 1-800-940-8924 for expert service.
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  • Reviews (639)
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  • Videos (2)
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Redline Trailer Leaf Spring Suspension - APUBR-1

  • U-Bolt Kits
  • Axle Mounting Hardware
  • Round Axle - 2-3/8 Inch
  • 5-1/2 Inch Long
  • 3500 lbs
  • 1/2 Inch Diameter
  • Redline

Mount your round, 2-3/8" diameter axle to your trailer's leaf springs with this U-bolt kit. U-bolts, plates and nuts included.


  • Attaches trailer axle to leaf springs
  • Includes:
    • (4) 5-1/2" Long U-bolts (176400)
    • (2) U-Bolt plates for 1-3/4" springs (117595)
    • (8) 1/2"-20 Hex nuts (12N)
  • Spring seats required for mounting axle to leaf spring sold separately


  • Axle diameter: 2-3/8"
    • Typical 3,500-lb axle
  • Spring width: 1-3/4"
  • Dimensions: see below

U-Bolt Diagram

APUBR-1 U-Bolt Kit for 3,500-lb Round Trailer Axles

Video of U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Trailer Axle Long U-Bolt Mounting Kit Review

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 Reviews

U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts - APUBR-1

Average Customer Rating:  4.9 out of 5 stars   (639 Customer Reviews)

Mount your round, 2-3/8" diameter axle to your trailer's leaf springs with this U-bolt kit. U-bolts, plates and nuts included.


It was so nice to work with new and proper fitting mounting bolts. Everything I needed to attach the axles was in the kit.


Parts fit as advertised, very satisfied with purchase. I new nothing about replacing a trailer axle info on web site and support provided were excellent.
Definitely would recommend etrailer


My boat trailer suspension repairs were made easy by your well designed website with complete descriptions and your prompt delivery of the correct, much better than the original equipment parts. I could have had a couple more weeks of fishing had I found you sooner. Thanks.


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.


Number one quality parts. Had to replace the axle due to lack of lubrication of the wheel bearings. Love the concept and ease of keeping the wheel bearings supplied with fresh grease on the e-z lube axles.


I replaced the rusted out U bolts on my 5x8 utility trailer with this kit, APUBR-1 from Redline. The kit fit great, no problems. Good quality parts. Great price. Would buy from etrailer again.


Great fit, easy to install. Upgraded from a single taper leaf to a quad leaf spring, on a Tracker Pro Team 175 TXW Bass Boat trailer.


Easy to install


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.


Quick delivery!

Excellent! Greatly improved the towing ride!
Mike - 05/25/2022


Joann was very knowledgeable and very helpful.. my trailer axle and parts arrived on time and everything was in doesn’t get any easier..


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...


Same parts I bought locally but since I was buying the new axle from E-trailer it saved me a separate trip. All installed easily and trailer is ready for service again.

Working as it should, good replacement product.
Ronald E - 08/13/2021


I am building my daughter and snl a kayak trailer so i ordered some new ubolts and plates. fit like a glove. Etrailer has what i9 want every time.


Just as described.


You didn't have in stock what I needed you had something else that worked even better thank you so much


they fit as were suppose to fast shippi ng


These were what I needed to replace my leaf springs on my 2800 lb dexter axle.


Great value

Still working as they should
Steven - 03/03/2022


Fit perfectly for my trailer. All the components seem to be heavy duty.

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.
Sgtbass64 - 12/09/2016


Etrailer made my purchasing and acquiring the parts I needed very easy. Customer service was exceptional!


I thought they were going to be short, turns out they were perfect. Good job. I bought a trailer for $350.00 now after replacing the suspension and going over the axle I think it might be worth $1000.


heavy duty U-bolt kit made installation easy with no worries!


The replacement trailer spring set was out of stock but Michelle watched for it with care and kept me informed. She let me know when it came in, shipped it quickly and made sure I had all the nuts and bolts needed to replace my broken springs. Have ordered from etrailer in the past and the quality and price can't be beat.

Awesome - use the trailer in salt water now and it is just as tight as ever. Thanks!
Gary L - 09/18/2020


Using has been a great experience. They have a huge selection of trailer parts and make it very easy to find the right parts. The packaging seems to have gotten alot better. Very sturdy box. It arrived within a few days from ordering which was a huge plus. I was able to get the job done sooner than planned. That kind of experience will keep me loyal to etrailer for any future trailer parts needs. Thanks guys and gals. Keep up the great work. As far as the parts, eveything was heavier duty than factory. Since I measured the old parts I was able to find the exact replacements for those parts. The job went so smoothly without any issues. These springs raised the trailer height without any load on the axles 1.5 inches. It was definitely time for new springs and hardware. Im kind of glad the one spring broke.

Show More Reviews

Ask the Experts about this Redline Trailer Leaf Spring Suspension

  • Choosing a U-bolt Kit for Trailer with 1-3/4 Inch Wide Leaf Springs
    When choosing a U-bolt kit for you trailer, you want to choose the correct kit based on the size of your trailer's axle. The width of the leaf springs isn't the main factor. The U-bolt kits you referenced will not both work on the same trailer axle. The # APUBR-8 kit can accommodate both 1-3/4 inch and 2 inch wide springs, but it is designed for use on 3 inch diameter round trailer axles that have capacities between 5,200 pounds - 7,000 pounds. The # APUBR-1 kit will accommodate 1-3/4...
    view full answer...
  • Kit Needed to Move Trailer Leaf Springs Back Under Axle
    If the leaf springs for your trailer are currently installed so that they are sitting on top of the axle, you can just use a standard U-Bolt Kit to move the leaf springs back under the axle. For a 2-3/8 inch, 3,500 pound axle, you will need the Redline U-Bolt Kit # APUBR-1 and for 3 inch axles with 5,200-7,000 pound capacities, you will use # APUBR-8. I have also attached a helpful installation video for you to check out.
    view full answer...
  • Torque Specs for U-Bolts on 3,500 Pound Axles
    For 3,500 pound axle U-bolt kits like the Redline # APUBR-1 that use 1/2 inch hex nuts you will want to torque them down somewhere between 45 and 70 foot pounds. I have attached a great article on trailer suspension that includes this info along with details on all the other necessary components that you can look through.
    view full answer...
  • Longest 1/2' U-Bolts Available for 3,500 Lb Round Axle
    The longest u-bolts we currently offer in 1/2" for a 2-3/8" diameter axle is 5-1/2" such as the U-Bolt Kit part # APUBR-1.
    view full answer...
  • Finish of Redline U-Bolt Kit # APUBR-1
    The # APUBR-1 U-bolts are constructed of steel, and the parts have a raw finish. They are coated with a light film of oil to help inhibit corrosion during storage.
    view full answer...
  • Should I Replace the U-bolts When Replacing the Leaf Springs
    I would not recommend reusing your existing u-bolts because the nuts are designed to mis-align the threads as they are tightened down to prevent the u-bolts from coming loose. You should choose the u-bolt kit that will fit the diameter of your axle. The u-bolt kit # APUBR-1 that you referenced is designed for one 3,500 lb trailer axle with a diameter of 2-3/8 inches. The kit includes 4 u-bolts, 2 u-bolt plates and 8 hex nuts 1/2 inch.
    view full answer...
  • What is the Torque Rating for 1/2 Inch U-Bolts for Leaf Spring Trailer Suspension
    The torque rating for 1/2 inch u-bolts in U-Bolt Kit, # APUBR-1, is a minimum of 45 ft lbs and a maximum of 70 ft lbs.
    view full answer...
  • Can the U-Bolts of the U-Bolt Kit # APUBR-1 be Cut 1/2 inch Shorter
    We can't cut the U-bolts of the U-Bolt Kit # APUBR-1 1/2 inch shorter. But you certainly can if you have a grinder or know someone who does. It would be pretty easy to do, especially if you have a cutting wheel.
    view full answer...
  • Parts Needed to Add Replacement Axles to Tandem Axle Trailer
    We do sell replacement trailer axles. To see if what we have would work for you, I'd need some information from you. I'll need the following: - Hub face to hub face dimension -Spring center to spring center dimension - Axle capacity - Reference numbers from inner and outer wheel bearings With this information, I'd be able to check to see if one of our axles would work for you.
    view full answer...
    Image 1 for
  • Torque Specifications for Redline U-Bolt Kit APUBR-1
    The torque rating for the 1/2 inch diameter u-bolts in the U-Bolt Kit # APUBR-1 is a minimum of 45 ft lbs and a maximum of 70 ft lbs. These are designed to mount your trailer's leaf springs to round, 2-3/8 inch diameter axles. The U-bolts, plates and nuts are all included in this kit. I have attached a couple of videos on this product so you can look at the installation process and see exactly what all is included in the kit.
    view full answer...
  • Are U-Bolts Includes with Trailer Axle
    The trailer axles we currently have available do not include the U-bolts necessary to mount the axle to the leaf springs on your trailer. The U-bolts you need will depend on the size of axle you are purchasing, along with its capacity. I have attached a couple links that will take you to our available selection of trailer axles and U-bolt kits that you can look through. If you can tell me what type of axle you are getting, I will be happy to recommend a kit that should work nicely.
    view full answer...
  • Torque Specs for U-Bolts on LoadRite Boat Trailer
    The correct torque spec for trailer suspension u-bolts will depend on the the diameter of the bolt. You will want to use the following depending on bolt size: 1/2" bolts: 45 ft/lbs - 70 ft/lbs 9/16" bolts: 65 ft/lbs - 95 ft/lbs 5/8" bolts: 100 ft/lbs - 120 ft/lbs 3/4" bolts: 140 ft/lbs - 160 ft/lbs The U-Bolt Kit part # APUBR-1 that you were referencing will need to be torqued to 45 ft/lbs - 70 ft/lbs as they are 1/2" diameter bolts. There should not be any space between the u-bolt plate...
    view full answer...
  • Grade of U-Bolt in the U-Bolt Kit APUBR-1
    The U-bolts of the U-Bolt Kit part # APUBR-1 are Grade 5. I attached an install and review video for this kit for you to check out as well.
    view full answer...
  • Longest U-Bolt Kit for Trailer Axles that are 2-3/8 inches in Diameter
    The inner width of the U-bolt needs to match the diameter of the axle that you have. The longest kit we have that has a 1/2 inch diameter studs is the part # APUBR-1 which has U-bolts that are 5-1/2 inches long.
    view full answer...
  • Installation of the U-Bolt Kit for Mounting 3500 lb Round Trailer Axles
    The U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts # APUBR-1 do not have a specified torque from the manufacturer. I did some research online and it appears that about 72 ft lbs would be appropriate for the 1/2 inch diameter nuts on the U-bolts.
    view full answer...
  • U-Bolt Kit Recommendation for 3,500 lb Trailer Axle that is 2-3/8 inch In Diameter
    The part # APUBR-1 is available through us. It is a U-bolt kit for 3,500 lb axles like what you have which are rated for 3,500 lbs.
    view full answer...
  • What Grade is the U-Bolt of the U-Bolt Kit part # APUBR-1
    The U-bolts of the U-Bolt Kit part # APUBR-1 are Grade 5. The torque range is minimum of 45 ft lbs and a maximum of 70 ft lbs. I attached an install and review video for this kit for you to check out as well.
    view full answer...
  • Replacement Axle for 1993 Western World Tandem Axle Trailer
    We do sell some replacement trailer axles. To see if what we have would work for you, I'd need some information from you. I'll need the following: Hub face to hub face dimension Spring center to spring center dimension Axle capacity Reference numbers from inner and outer wheel bearings With this information, I'd be able to check to see if one of our axles would work for you.
    view full answer...
    Image 1 for
    For the large 8000 lb. springs you want to use U-Bolt Kit for Mounting 8,000-lb, Round Trailer Axles part # APUBR-35 and for the smaller 3500 lb. springs use the U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles part # APUBR-1. Thes will give you the u bolts, nuts and the new plates so you will be set.
    view full answer...
  • Can a Three Leaf Spring Stack Be Used To Replace a Two Leaf Spring Stack
    Yes, you can replace a two leaf spring stack with a three leaf spring stack so long as your center to center (double eye springs only) measurement matches but please note the loaded and unloaded as well as the new and used center to center measurements will be different. There is a correlation between the numbers of leaves in a stack and the weight capacity of that stack but there are also two leaf spring stacks with the same weight capacity as three leaf spring stacks so going by the rated...
    view full answer...
  • How to Pick Out Slipper Spring Suspension Equalizers
    If your trailer suspension seems to be in good shape, other than the broken equalizer, then you do not have to replace both sides if you do not want to. The best way to find the correct replacement equalizer is to measure the shackle bolt holes and make sure you choose the correct style equalizer (double-eye vs. slipper). What you will want to do is check out the link I attached that has all of the slipper spring equalizers we carry. You will need to find the shape of your equalizers...
    view full answer...
  • Recommended U-Bolt Mounting Hardware for 3,500 lb Axles
    It sounds like you have 3,500 lb axles that are typically 2-3/8 inch diameter and could easily be rounded up to 2.5 inches. For your U-bolts, I recommend the CE Smith U-Bolt Kit- Zinc # CE230025 for the increased corrosion resistance or the U-Bolt Kit # APUBR-1 for basic mounting kit. I've attached some videos to assist.
    view full answer...
  • Should I Paint U-Bolts to Protect Finish
    If you are concerned about rust and corrosion, an excellent option for you is the CE Smith U-Bolt Kit for Mounting # CE23002 which comes with galvanized plates and zinc-plated hardware. The u-bolts included are also 5-1/2 inches long and 1/2 in diameter just like in the APUBR-1 kit. You can apply a coat of rust-resistant paint to the U-Bolt Kit # APUBR-1 if you want to but it's not required. In fact, most people don't because these components, while susceptible to rust, are not directly...
    view full answer...
  • U-Bolt Plate Width For Leaf Spring Mounting on APUBR-1
    The width dimension of the U-Bolt Kit for Mounting 3500-lb Axles # APUBR-1 is 2-3/8", which is the typical diameter of a 3500-lb axle. These can be used to mount leaf springs 1-3/4" wide to an axle when used with with the included plates and Spring Seat for Typical 3500-lb Round Trailer Axles # TRSS238 . I've attached a picture for reference on these measurements.
    view full answer...
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