Flusso 150.4500T Trim For Thermostatic ValveHandle Operation The middle handle is used to control the temperature of water flowing through the outlet. The top handle can control the volume of water from full flow to a trickle for various output ports. The bottom handle can control the volume of water from full flow to a trickle for the various output ports. Cut Out Dimensions The cut out in wall should be 8. 81 X 4. 44 Inches and no more this will ensure that the trim plate will cover the cut