Bridges interior of gutter, largely hidden from view, but interferes with cleaning. Hangers with built-in screws (shown) hold better than spikes and don't mar gutter faces.
Pro advice: To drain properly, a gutter should slope at least ¼ inch for every 10 feet of run. Increasing the pitch increases a gutter's handling capacity, but the gutter may look askew over a long run. The easiest way to check pitch: Dump in a bucket of water and watch how it flows.
—Gene Stucky, Park City Rain Gutters