The purpose of this document is to aid the gear designer in understanding the unique physical, mechanical and thermal behavior of plastic materials. The use of plasticmaterials for gear applications has grown considerably due to cost and performance issues. Growing markets include the automotive, business machine, and consumer - related industries. Topics covered include general plastic material behavior, gear operating conditions, plastic gear manufacturing, tests for gear related material properties, and typical plastic gear materials. There are no quantitative details on material properties nor any comparative evaluations of plastic types. Such specific information is left to be provided by material suppliers and gear manufacturers.