Coldworking holes is an established manufacturing procedure in the aerospace industry. There are two coldworking methods used today: split-sleeve and split-mandrel. The intricate steps of these processes are not completely understood. There has been no investigation into the differences in the mechanisms of the two processes. Initial results from an ongoing program reveal that the differences in the mechanisms impart the split-mandrel process with advantages over the split-sleeve process, including the ability to coldwork 7000 series aluminum without shear cracking at the axial ridge, and the ability to effectively automate the process.