US Patent 7654792 Blower

Blower made up of at least two axially stacked, interlocking fans. Each fan is enclosed in a housing the axially opposite ends of which are flanged. Opposing flats on immediately neighboring flanges are formed with complementary twist-locking features. The twist-locking features are configured in such a way that when the fans are stacked, the opposing flats will not be in contact with each other unless the housings are twisted out of axial alignment to bring the opposing flats flush together, and such that with the opposing flats flush in contact, twisting the housings back into axial alignment locks them together.