Feature: 1. Made of high quality ABS plastic, this product is sturdy and durable. 2. The inner side is smooth and the bell ends are designed at both ends. The airflow is very smooth and the airflow is obviously improved. 3. The height of the inverted tube is 90MM and the opening is 76MM. It is suitable for speakers with 4-8 inch speakers. 4. Speaker inverting holes, also called sound tubes and air holes, are often used in inverted speakers. 5. The sound pressure of the airflow vibrating in the box is poured out to overlap the sound pressure radiated in front of the speaker to produce a bass effect. Specification: Item Type: Inverted Tube Height: Approx. 90mm / 3.54in (as shown in picture) Opening: Approx. 76mm / 2.99in (as shown in picture) Package List: Inverted Tube x 4