This 331 Number 3 Pneumatic Damper Actuator is a rugged, metal-fabricated device that provides gradual or positive actuation of HVAC dampers. This actuator has a nominal spring range of 8 to 13 psi, is fixed bracket mounting and has an ozone-resistant rolling rubber diaphragm. This actuator has an air connection of 1/8" NPT female with a straight dual barb fitting for 1/4" OD tubing