Seed ports below the perches allow goldfinches to hang upside-down to feed, which house finches can't do. Cap lifts off easily for re-filling and thorough cleaning. The design of the cap makes it difficult for predators to lift and reach the seed. Cap, base, perches and hanger are metal. UV-stabilized polycarbonate tube. Dimensions: 16" H (plus 4.5" hanger) x 2.5" diameter tube. By Droll Yankees.