Many wind instruments have some kind of flaring bell shape. The smooth fertile surface is on the interior of the bell shape. It does not contract into a bell shape when stimulated. The bell shape widens as the altitude diminishes. The gearbox itself was of a bell shape with only five gears. However, the third virial coefficient has a bell shape. Skirts had developed an overall bell shape but with extra fullness at the back. The bell shape of the inflorescence is likely to protect the flowers from rain. As such, the inverted bell shape is a popular form used with planing hulls. Cedrosan Saladoid vessels have a distinctive bell shape with "zone-incised cross-hatching".