Oil cap for Honda/Acura cars. It should fit to most models with threaded oil cap with 32mm diameter.
I tested it with my 1996 Honda Civic with D-series engine.
NOTE: Keep in mind that engine valve cover can get very hot thus I can't recommend it for daily use (neither do I) especially if you print it with PLA or other material with relatively low melting point.
I designed it for emergency purpose when I lost my oil cap and used it for short trips before I got new one.
Since this is more about functionality than a design, I printed it with 0.2mm resolution and it works well. 20% infill seems to be enough to maintain the strenght.
I designed it with Tinkercad. It's pretty simple but functional design. The only difference between versions is cap diameter 45 or 75 mm.