This is an adapter for the later model TJs (probably 2003-2006) that enables the use of a cabin filter for the HVAC system. These Jeeps never had cabin air filters, which means all the dust you eat on the road or trail ends up being blown over you in the cabin. This allows use of a single late-JK air filter cartridge.

The proper air filter model is Fram FDC11777, but any other brand that claims to work for a 2011-2017 Jeep Wrangler should work. They come in pairs (because the JK uses two at a time) but you only need one for this model.

Simply remove the cowl between the windshield and hood, remove the factory duct (if present) and install this adapter place in its place. One of the air filters drops into place (be sure to respect the air flow direction arrows on the filter).

This is made from two pieces for printability. The “base” is an adapter that goes around the factory flange and provides a flat surface for the “filter holder” to sit on. My printer was too small to fit either piece on the build plate, so there is another variant of this that is split into four files so that you can print them in pieces. In that case, the pieces are indexed so you can make sure they stay together. Some glue can be used to seal it all up but the screws and indexing will keep the thing together sufficiently well without it.

You'll want to print this in something temperature-resistant of course, ABS/ASA or PETG. The picture is regular black ABS with 0.3mm layers, 2 top/bottom layers and 30% cubic infill. It's not pretty due to the thin top and bottom, but it's more than strong enough that way.