Colorbond Matt Half Round External Cast Corner 90 deg to fit half-round gutters. Colorbond Matt Half Round Gutter is attractive and largely self-cleaning. With a diameter of 150mm, it can carry a lot of water. Because of its practical shape, the Half Round is ideal for modern homes and commercial buildings. Gutter miters can be easily solved with pre-made cast external corners. Providing a clean, modern look around the corners of a building, they are neat, practical, and aesthetically pleasing.