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A secure axle mount is key to safe towing. This kit locks your axle to the springs with four 9/16"-diameter, Grade 5 steel U-bolts. Each one provides a strong clamp for 3" round axles rated from 5,200 lbs to 7,000 lbs. When torqued between 65 and 95 ft-lbs, they hold firm without bending the plates, keeping your suspension tight and steady mile after mile.
Getting the geometry right matters for ride height and handling. These 7-1/16" long U-bolts are made for 3" diameter round axles and work with 2" wide springs. The plates are drilled for a clean fit, with 3-3/4" center-to-center spacing between holes and 2-5/8" between the spring bolt locations, so everything lines up just the way it should.
You don’t have to chase down missing pieces. The kit includes four U-bolts, two heavy plates for 2" springs, and eight 9/16"-18 hex nuts. Everything threads together cleanly with 3" of usable thread length per bolt, giving plenty of bite for reliable torque and even pressure across the assembly.
If you’re raising your trailer with lift blocks or taller spring hangers, these U-bolts have the 7-1/16" length to handle the extra space. They give you the reach needed to tighten down securely without running short on threads, making them a versatile choice for upgrades or maintenance on high-capacity setups.
Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Today we'll be reviewing Part Number APUBR-9. This is Red Line U-Bolt Kit for mounting 5200 lbs to 7000 lbs round trailer axles. It's going to attach the trailer axle to your leaf springs, it's going to include four 7 1/4 U-bolts, 2 U-bolt plates for 1 3/4 inch or 2 inch springs, and then it's going to include eight 9/16 inch hex nuts. Spring seats are required for mounting the axle to the leaf springs and that's all going to be sold separately. It's going to fix axle diameters of 3 inches, typically 5200 lb to 7000 lb trailer axles. The spring width that this would fit is going to be 1 3/4 inch or 2 inch and we'll just take a few moments to go over some dimensions. We take a measurement of the length of the u-bolt, again we're measuring from the bottom of the cross member, to the base of the bolt post.
It's going to give us a measurement of 7 1/4. The threaded portion on each bolt is going to measure 3 inches. It's that portion there and then the width that we have in between is going to measure right at 3 inches and that's just a measurement between the bolt posts. Taking a look at one of the plates, it's going to measure 5 1/4 by 3 3/4. We measure the distance, center on center between the holes going this direction, it's going to measure 3 3/4 of an inch and then center on center going this direction is going to give us a measurement of 2 5/8 of an inch. That's going to do it for our look at Part Number APUBR-9, this is Red Line U-Bolt Kit for mounting round trailer axles and again the bolts are going to measure 7 1/4 of an inch in length.
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Customer Satisfaction Score:
98% were satisfied with this product
2% of customers were not satisfied
Ratings & Reviews
Mike L.
6/25/2026
Thanks David, we appreciate the kind words!!
Brooke M.
2/17/2025
The photo looks great! Thanks for sending it in. So glad youre happy with it! :)
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Gwendolyn Y.
5/20/2026
Thanks for the awesome detailed review, Kevin! Really glad Kyle and Daylon were able to help track down the issue and get you pointed toward the right setup. It sounds like you put a lot of care into the install, and it definitely paid off. Making use of those stumps was pretty genius too. Safe travels ahead!