The chimney reducer for the Squape A[rise] is used in combination with the MTL or RDL air discs to ensure a smooth and consistent vape at all stages of airflow. Amazing system for MTL conversion, as the A[rise] with MTL discs and chimney reducer easily rivals any of my Kayfuns for a flavourful, smooth, and tight MTL experience. To install this, simply remove your 510 drip tip, drop the reducer into the chimney, and place the drip tip back over top. No rattling, and it's easy to remove. I believe the bore of the reducer is 3mm, so it can also be used in RDL mode as long as your chosen RDL air disc is 3mm of airflow or less.