OKIDATA ML320 Turbo Service Manual page 41

(4) Pull tractor (option) and push tractor operation (See Figure 2-11)
This mechanism supports the standard push tractor and an optional pull tractor. It can perform forward
and reverse feed by sending paper either to the push tractor (for rear feed) or to the pull tractor (for bottom
feed).
The rotation of the platen is transmitted to the push tractor and the pull tractor. Paper can be fed to either
tractor.