These 'cymbals' follow the same principle as a pair of normal hi-hats, except they are made from two matching flywheels. A flywheel is a metal plate that connects the crankshaft of an engine to the torque converter of an automatic transmission. It also has a ring gear that the starter motor engages with. These two flywheels were leftover after I replaced the engine in a Nissan Altima.
Here is a flywheel on the back of an engine. The transmission has been removed.
The flywheels needed to be adapted so they could be mounted on a traditional hi-hat stand.
The bottom flywheel rests on the hi-hat stand, and the upper flywheel is attached using a standard hi-hat clutch.
When played with the foot pedal they are kind of loud and clangy, but they have a good sound. They can be played with drumsticks like normal hi-hat cymbals. It also works well to 'splash' them with the foot pedal.