ELECTROMAGNETIC KITCHEN VENT AP500 - GMC MOTORHOME Electronically controlled with strong magnet. Magnet is strong enough to keep the flapper airtight even in strong winds and reduces outside noise. Turn on the fan and push the release button to pop open the flapper. Highly recommended side vent. inside mounting dimensions approx 10 7/16" x 3 1/2" outside dimensions: approx 12 1/2 " x 6"