The function of a sheath is to protect the knife and its user whenever the knife is not being used. A knife can be hung on a belt from the sheath's loop. A sheath is always custom designed for each knife model. The fine details on a sheath are decorative, but they often have a practical significance as well. For instance, the triangular piece of leather at the tip of many sheaths prevents the distracting back and forth motion of a sheath hung on a belt when walking.