Bass drum hole accessory, red color, said to be eye-catching and cool. For use as a bass drum subwoofer. Cylinder diameter is about 10.6 cm, and a hole of about 11 cm needs to be made. Instructions on how to make the hole can be found on YouTube, etc. A compass cutter is commercially available (500 yen extra if needed, please contact me). To cut and install, remove the head first. Peel off the round film of the gasket and attach it to the head surface. Insert the main body cylinder and insert the rubber from the back. It's easier to do this with water. Attach a microphone and connect it to an amplifier (photo). Adjustments are made on the amplifier. It's better to have two people do it and have someone listen. No profit. Ready to ship immediately.