These are popular, standard inner baffle boards for improving the sound quality of car audio systems. This product is a set of 2 universal type boards. The sound quality of your audio system deteriorates due to sound reflection and interference caused by the car's vibrations and the speakers inside the door. However, by using inner baffles, you can prevent vibrations and interference, and improve the sound quality, especially the bass. This product is used by sandwiching it between the door speaker and the door's metal plate. 【Compatible Vehicles】 This is a universal type, so it is compatible with many vehicles (16cm, 17cm, 6.5-inch speakers). It can be used in various vehicles if the size fits, such as Daihatsu, Suzuki, and Mazda. Please be sure to check the size before purchasing. There are no fixing holes, speaker recess, or wiring escape holes, so please process them before use. 【Size】 Outer Diameter: 18.5cm (185mm) Inner Diameter: 14.5cm (145mm) Thickness: 15mm 【Material】 MDF