The Original Adult Propeller Cap Made In the USA. This is the finest product in this category by far. All the others are cheap knockoff versions of this cap which are all made in China and they are sure to disappoint. The Interstellar Propeller cap is made in the USA and is the only high quality adult propeller hat you will find. It was originally designed by the legendary Wavy Gravy in 1975 and has stood the test of time.