Stones whose outlines are either square or rectangular and whose facets are rectilinear and arranged parallel to the girdle are known as "step-" or "trap-cut" stones. These stones often have their corners truncated, creating an "emerald cut" (after its most common application to emerald gemstones) with an octagonal outline. This is done because sharp corners are points of weakness where a diamond may cleave or fracture. Instead of a culet, step-cut stones have a "keel" running the length of the pavilion terminus. Like other fancy shaped diamonds, emerald cut diamonds can come in a variety of length to width ratios. The most popular and classic outline of emerald cut diamonds are close a value of 1.5.