Presents a new basic rack@ AGMA PT@ which@ with its full round fillet@ may be preferred in many applications of gears made from plastic materials. It contains a description@ with equations and sample calculations@ of how the proportions of a spur or helical gear may be derived from the design tooth thickness and the basic rack data. In several annexes@ there are discussions of possible variations from the basic rack and also a procedure for defining tooth proportions without using the basic rack concept.