This vacuum adapter piece is for anyone who owns a different brand of vacuum that comes with a 2-1/2 in style vacuum hose. We have taken multiple measurements to show you the closest diameter measurements in inches of the different vacuum hoses. The black adapter piece should slide in and create a tight seal with the vacuum hose. We recommend purchasing SurfPrep's vacuum hose to screw into this vacuum gray part of the adapter piece. Other brand of vacuum hoses can actually be very heavy, so we recommend purchasing a 12 ft long SurfPrep hose to attach to this piece.