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SAE J635 2014 Edition, March 1, 2014
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Fan Hub Bolt Circles and Pilot Holes
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AIA/NAS Aerospace Standards
This Recommended Practice applies to engine cooling fans up to 2000 mm in diameter with a mounting interface consisting of a pilot hole and a circular bolt pattern. Most of these fans are belt, gear, clutch, hydraulically, or electrically driven.


The purpose of this SAE document is to encourage the standardization of mounting patterns for engine cooling fans. A secondary purpose is to encourage adoption of SI metric units, although a listing of existing common English unit mounting patterns (legacy patterns) is provided. It is specifically not the objective of the specification to address the soft metric conversion of existing mounting patterns on engines designed in English units. Adherence to this specification should result in cost savings through reduction of part numbers and inventory, and more robust fan design. Failure to comply with this specification will result in the need to release and carry in inventory parts of identical blade geometry and construction, but with different mounting patterns.