♦ New 77mm to 82mm Step-Up Ring Adapter- The 77-82mm ring adapter easily screws onto the front of any 77mm lens, and converts the thread size of your lens to the thread size of any other 82mm accessory (such as filters, hoods, flashes and lens converters).- Made of high quality anodized black alumin...

The pressure switch is also referred to as a combustion air switch or draft proving switch. 1.74. Switch closes when the combustion/booster motor runs creating a negative air pressure.