A downhole tool anchor is disclosed. In one implementation, a downhole anchor tool may include a housing, an axial drive in the housing, a rack connected to the axial drive, a pinion in the housing, the pinion having teeth that engage teeth on the rack, a gear tube within the pinion, the gear tube having internal threads, a slip rod having external threads that engage the internal threads within the gear tube, and a radial bearing coupled to the gear tube, the radial bearing having a slip rod alignment member that prevents the slip rod from free spinning in the gear tube.