Stop valve designed to work in conjunction with any 3" piping, hose or duct inlet/outlets. 

This valve allows you to vent without exposure to outside air/critters when the fan is not in use.

For the updated quick release variant see:

'Quick Release' variant update:

The new version of this model has been completely redesigned to eliminate the threaded stem in order to provide a simplified user experience with numerous additional updates and refinements including reduced support requirements, as well as updated geometry and tolerance refinements. As a result, I highly recommend printing the quick release variant over the threaded variant.

Specs:

Outlet (male): 2.9" OD

Inlet (female): 3" ID

Assembly:
Simply Insert the valve disk through the inlet end of the valve housing, and screw the stem/handle onto the valve disk.

Disk and Stem feature an aligned hole. You can use a toothpick, or a similarly sized object in order to lock the disk in place in order to avoid unwanted rotation of the disk off the stem during operation. You can also use a small amount of super glue during assembly, or both.

Print:

The parts were designed to require as little supports as possible, but you do still require a small amount of supports to support the T section of the 2 inlet overhangs (once on the lower exterior and once on the upper interior). The use of supports for the upper interior inlet overhang in not mandatory, however this may cause some small visual sagging on the upper interior wall of the inlet which does not effect the functionality of the part and reduces print times greatly.

See the link below for a compatible duct adapter:

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Enjoy!