The Dillon Powder Die is used to hold the powder measure. The powder die screws into the tool head of your favourite Dillon progressive reloading machine and the powder measure attaches to the powder die. Additional powder dies allow you to share powder measures between calibres, while retaining the difficult -to-set flaring / belling adjustment.
The powder die is also used to hold the powder check system for the Dillon XL 650 and Super 1050 progressive reloading machines. So, sharing the sensor between tool heads becomes viable with additional powder dies.