ATNVIDSG Roof Box U-Bolt Clamps — 85mm Universal Stainless Steel 4‑Piece Mounting Kit

ATNVIDSG Roof Box U-Bolt Clamps are a 4-piece stainless-steel mounting kit designed to securely attach cargo boxes to most 85mm-width roof racks without drilling.

These U-bolt brackets and accessories give a simple, reusable way to fasten a cargo box to a vehicle’s crossbars. Built from stainless steel with rubber gaskets and plastic backing plates, the kit balances corrosion resistance and vehicle protection. It comes with all necessary hardware — U-bolts, washers, back plates, lock nuts, straps and a sealing sticker — so you can mount or remove a roof box quickly while keeping scratches and movement to a minimum.

How do these clamps fit different roof rack sizes?

The clamps are made for crossbars with an inner gap of about 85 mm and an outer width near 90 mm, and they accept bar thicknesses up to roughly 40 mm. Check your rack’s inner width and thickness before ordering to ensure compatibility.

• Inner width: 85 mm (3.35 in)
• Outer width: 90 mm (3.54 in)
• Accepts bar thickness: up to ~40 mm (1.57 in)
• Includes two adjustable straps for added hold

What materials and protections are included?

The kit uses stainless steel for the U-bolts and durable plastic for backing plates, paired with rubber gaskets to protect paint and increase grip. These materials resist rust and deformation, helping the hardware last through seasonal use.

• Stainless-steel U-bolts resist corrosion
• Rubber gaskets cushion and prevent scratching
• Plastic back plates distribute clamping pressure
• Sealing sticker helps protect the roof hole area

How hard is installation and what comes in the box?

No drilling is required: the parts are designed to clamp around existing crossbars and secure with supplied lock nuts. The set includes everything needed to mount a typical cargo box, and instructions are straightforward for a DIY install.

• 4 stainless-steel U-bolts
• 4 rubber washers and 4 plastic back plates
• 8 lock nuts and 2 long straps
• 1 hole sealing sticker and simple fitting steps

Will these clamps keep my cargo box stable on rough roads?

The combination of secure U-bolts, anti-slip rubber, and supportive back plates reduces shifting and helps maintain a stable load through bumps and turns. Straps add redundancy to prevent loosening while driving.

• Rubber increases friction to limit sliding
• Back plates spread load to prevent concentrated pressure
• Lock nuts secure hardware against vibration
• Straps provide secondary restraint for safety

Who is this for: The ATNVIDSG Roof Box U-Bolt Clamps suit drivers who need a universal, non-permanent mounting solution for rooftop cargo boxes—especially owners of crossbar systems around 85 mm inner width who want corrosion-resistant hardware, protective gaskets, and complete installation parts in one compact kit. Before purchasing, measure your crossbar inner width and thickness to confirm fit. If you need additional help choosing the right size or have fitment questions, reach out to the seller for guidance.