API Standard 677 covers the minimum requirements for general-purpose, enclosed single and multistage gear units incorporating parallel shaft helical and right angle spiral bevel gears for the petroleum, chemical, and gas industries. Gears manufactured according to this standard shall be limited to the following pitchline velocities. Helical gears shall not exceed 60 meters per second (12,000 feet per minute), and spiral bevels shall not exceed 40 meters per second (8,000 feet per minute). Spiral bevel gearsets shall be considered matched sets.

This standard is not intended to apply to gears in special-purpose service, which are covered in API Standard 613, to gears integral with other equipment, to epicyclic gear assemblies, or gears with non-involute tooth forms.

Typical applications for which this standard is intended are cooling tower water pump systems, forced and induced draft fan systems, and other general-purpose equipment trains