I'm a sparky by trade and have struggled to get a good air-tight seal around conduits when pulling a string line through for long cable pulls. I designed this to fit within a 150-mm HD conduit and attach to a vacuum with a nozzle of 32mm (or a piece of 32-mm conduit that can be taped onto or adapted to fit.) The opening size at the bottom is 120mm, meaning any smaller conduit can also be used to a minimum of 32mm.