Is the 40-inch measurement the internal or external length

and MSZ-D30NA

this relay is a direct replacement part for maintaining system safety and efficiency

this specific model is calibrated and orifice-matched exclusively for liquid propane (LP)

The MARS 12078 is a round-case design

Siemens Building Technology 331-2904 Actuator 321142-301 Is the 40-inch measurement theThe Siemens 331 2904 is a heavy duty #4 pneumatic damper actuator designed for the gradual or positive actuation of large dampers in commercial ventilating systems. This piston type actuator features an all metal body construction and is specifically UL recognized for high stakes fire and smoke applications. With a 3 7 psi spring range and a generous 4 inch stroke, it provides the necessary force for reliable operation of outdoor air, return air, and