64mm interior diameter, 66mm exterior diameter, 42mm long. 24mm diameter motor mount with internal steps for 20mm motor. Remove these steps for use with up to 24mm dia. motor. Motor mount pattern is 4 holes on 16mm centers. This is the replacement fan for our Su-34, F-15, and F-86s jets. Accepts the HLI34360701 brushless Outrunner motor (sold separately). Includes collets for 3mm shaft motors. Includes 4-2.5mm motor mount screws.