A system for positioning a cartridge is disclosed. The system has a drive rod with a body having a first axis and a groove formed in the body. The groove has a first portion that is not perpendicular to the first axis and a second portion that is perpendicular to the first axis. The system also includes a collar that coupled to the drive rod. The collar has an element configured to engage the groove. Rotation of the drive rod with respect to the collar while the element is engaged in the first portion of the thread causes the collar to move with respect to the first axis. Rotation of the drive rod with respect to the collar while the element is engaged with the second portion of the thread causes the collar to remain stationary with respect to the first axis.