Stadium BM725 127mm Core Drill Black Hole Ventilator – 30cm² Anti-Draught Light-Blocking 5-13kW Stadium BM725 127mm core drill ventilator, packed with a Black Hole cavity liner, is what sets it apart from the standard BM418 core drill ventilator. The Black Hole design changes the direction of the airflow through the tube, slowing down the air that's coming in so you don't get a draught - and blocks out any light passing through to stop insects and vermin sneaking in. It has a 30cm² free area and comes in at 5-13kW net rated input. The adjustable tube length is between 228-585mm - meaning you can get it to fit most wall thicknesses without needing to add extra bits. The grille inside is white, and the bit on the outside is brown. The Black Hole liner really is what makes the BM725 different from the BM418. The BM418 has a plain old straight