This standard covers the minimum requirements for special-purpose@ enclosed@ precision single- and double-helical one- and two-stange speed increasers and reducers of parallet-shaft design for refinery services. It is primarily intended for gears that are in continuous service without installed spare equipment.Note: The purchase of a spare set of gear rotors or a complete gear unit does not mean that the equipment is spared.This standard includes related lubricating systems@ controls@ instrumentation@ and other auxiliary equipment. This standard is not intended to apply to gears in general-purpose service@ which are covered by API Standard 677 (inpreparation); to gears integral with other equipment; or to gears other than helical.Note: A bullet (?) at the beginning of a paragraph indicates that a decision by the purchaser is required. These decisions should be indicated on the data sheets (see Appendix A) when provisions are made thereon; otherwise@ they should be stated in the quotation request or in the order.The following gear-driven applications may be covered by this standard:a. Speed increasers@ including those for centrifugal compressors@ axial compressors@ blowers@ rotary positive displacement compressors@ contactors@ separators@ and centrifugal pumps.b. Speed reducers@ including those for reciprocating compressors@ rotary positive displacement compressors@ contactors@ centrifugal pumps@ extruders@ generators@ and fans.