Simply utilising the oligodynamic effect exhibited by silver (as well as copper and a few other metals).
Brass doorknobs naturally disinfect themselves in about 12 hours.
I naturally assume brass balls do so as well.
I think the real invention here is a way to get silver’s effect onto stainless steel in a way that it won’t rub off over time.
The funniest implementation of silver has been some guy in Japan who basically sewed silver fibers into underwear to reduce body odor.