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 cost-effectively! Definitely! I am confident in the quality that will satisfy you. Material: Birch plywood (15mm thick / Unpainted) Aperture: 140mm (for 17cm speakers) Included: M5 screws 30mm + special washers Free shipping, instant purchase OK Detailed specifications and features are summarized in the photos, so please take a look. I think even beginners can install it with confidence. If you have any questions, such as "Will it fit my car?" or if you want to discuss custom orders, feel free to comment. Also, if you would like to add other options, please comment and I will create a dedicated listing for you!