Style A-external hinge. Anodized heavy-duty aluminum frames. Heavy-duty acrylic top. No sharp corners to snag lines or sails. Heavy-duty hinges, quick acting, adjustable tie down dogs. Locked vent position.Cut Out 20-1/4" x 20-1/4"Flange 21-7/8" OD x 21-7/8" OD MFG# N103910A UPC# 759739000019