Siemens 331-631 DAMPER SHAFT EXTENSION, 1/2-INCHSiemens 331 631 Damper Shaft Extension, 1 2 inch This 1 2 inch diameter shaft extension facilitates the mounting of extended shaft damper motor assemblies to heating and ventilating or air conditioning units with short, extended damper shafts. This extension can be used on #3, #4 and #6 damper actuators. Additional Information Dimensions (W x H x D)2. 2 x 0. 5 x 0. 5 in