A spherical head with a hem, also called a butterfly head. Consisting of a spherical surface, a straight cylinder, a straight edge, and a transition part connecting the two parts above a radius of curvature smaller than the radius of the sphere. The dished head is a continuous curved surface. At the joint of the three parts, the radius of curvature of the warp has a sudden change, and there exists bending stress due to the change of curvature. The results of the superposition of bending stress and tensile stress make this part of the stress protrude out of other parts. Compared with the elliptical head, the stress distribution is not as uniform as that of the elliptical head, but it is easier to process than the elliptical head, so it is not ideal in the engineering application. But when the processing of the die of the elliptical head is difficult, the dished head is used instead. Implementation criteria: GB/T25198-2010.