A BLACK+DECKER delta sander (also known as a triangle sander or detail sander) can be used for sanding both flat surfaces and difficult-to-reach spots and nooks. This is useful if you're providing the stairs or windowsill with a new layer of paint or varnish. A delta sander has a triangular sole. As a result, you can use the wide part at the back for flat surfaces and reach the difficult nooks thanks to the point.