Materials: This U-Bolt is made of stainless steel. According to research, stainless steel has weak magnetism, so it also be attracted by magnets. High Quality:Roof box fitting is made of stainless steel, which is wear-, , not easy to break and deform, and has a long service life. Easy to Use: Roof box brackets are small-sized, and space-saving, can be placed in the room or in the car. The installation is simple and convenient, and it is convenient to use. Universal size: Inner width: 85 mm. The width from the center to the center of the thread is 90 mm, and the diameter of the screw is 7 mm. Can be used with roof reinforcement up to 40 mm thick. Specifications: 1. Suitable for luggage racks up to 40mm/1.57in thick 2. Internal width: 85mm/3.35in 3. bolts diameter: 7mm/0.28in 4. Center to center of screw width: 90mm/3.54in Step: 1. Lock the tensioner from the top or bottom; 2. Insert the pipe and lock it directly with the U-bolt and crossbar; 3. Input on rubber discs; 4. Put on the spring washers and fasten with nuts, then you are done. Material: metal Color: Black Package Contents: 1 set of luggage accessory kits Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.