COMPLETE KIT: Our roof box kit contains 4 stainless steel U-bolts, 4 rubber washers, 4 plastic support plates, 8 locknuts, and 2 fabric straps. High-quality material: galvanized steel and plastic, offering strong resistance to alkali, acids, corrosion, and temperature. Bolt diameter: 7 mm. Inner width: 85 mm. Center-to-center bolt width: 90 mm. Applicable size: can be used for steel bars up to 40 mm thick. Strong and sturdy: the thread is deep, clear, evenly tensioned, and difficult to slip. 85 mm inner width: our roof box kits fit most vehicles on the market. The center-to-center thread width is 90 mm. The bolt diameter is 7 mm. Not suitable for oil tanks. PREMIUM MATERIALS: Our roof box cleats are made of high-quality galvanized steel and plastic, making them durable, strong, and long-lasting. Safe Design: With ergonomic rubber seals and a plastic back panel, it protects your car from scratches and keeps your luggage secure. EASY TO USE: Our roof box kits are easy to install, lightweight, and compact enough to store easily in your room or car. Installation Steps: 1. You can lock the tensioner from the top or bottom. 2. Insert the tube and secure it directly with the U-bolt and crossbar. 3. Insert the rubber pan. 4. Install the spring washer and secure it with the nut. You're done!