<p>Many people know that you can install a cabin air filter in citybugs that didn't come with AC by cutting a hole in the air duct where it would be. But I tried this and found it very challenging to accurately cut the hole to fit the filter in the awkward space under the dash, so instead I cut it a little oversize and modeled this plate to use the two screw ports and accurately fit the filter's clips.</p><p>I screwed this in with two ‘number 6’ x ¾" countersunk self tapping screws. Similar sized screws will probably work. Screw holes are 4.6mm diameter. Print in PETG or another filament that's unlikely to warp in summer heat. If you want an airtight seal, maybe put some silicone sealant on the back of it before installing.</p>