This Demonstration models the deformation of noncylindrical springs under an applied tension load. An extension spring is designed to get longer when a load is applied to it. The spring coils can be cylindrical, with constant outer diameter of the windings, or noncylindrical, with variable outer diameter. Popular shapes for noncylindrical springs are hyperboloidal (hourglass/barrel) springs or conical springs. When a load is applied, a cylindrical spring has constant deformation of the windings over its entire length. Noncylindrical springs have variable deformation of the windings, depending on their diameter. Larger diameter windings deform more than smaller ones.