Thank you for viewing! ^_^ This is an inner baffle made of birch plywood. I also love audio and have used various inner baffles, but none of them satisfied me...(^^;; So, I started making my own. For those who want to improve sound quality effectively and at a good cost performance! Please! I am confident that it is a quality that you will be satisfied with. Material: Birch plywood (15mm thick / unpainted) Opening diameter: 120mm (for 13cm speakers) Included: M5 screws 30mm + special size washers Free shipping, instant purchase OK Detailed specifications and features are summarized in the photos, so please check them. I think even beginners can install it with confidence. If you have any questions, such as "Will it fit my car?" or if you have any special order requests, feel free to comment. Also, if you would like to add other options, please comment and I will create a dedicated listing for you. Thank you!