With any contained extrusion die, best results are often obtained by forming wire that is somewhat larger in diameter than the finished shank. Wire size is selected so that the upset dimension of the head will be about twice the original wire diameter. This wire is extruded to the shank diameter and upset to the head dimensions in the customary manner.
The fourth installment of this six-part series on heading basics will recommend practices when combining upset tings and extrusions and discussed warm and lot heading techniques.

楼主给的文章太专业了，我只能尽力翻译到这样：

当使用任何闭合式挤压模时，选择线径稍大于成品柄杆的金属丝成型效果最佳。选择金属丝尺寸时，原始金属丝之线径应当为头部镦锻直径的大致两倍。此金属丝被挤压到柄杆直径并镦压至定制之头部直径。

此镦压基础知识系列有六部分，第四部分将推荐一些镦压和挤压综合使用时的惯用技术，并讨论温锻压及热锻压技术。