Bearing balls are special highly spherical and smooth balls, most commonly used in ball bearings, but also used as components in things like freewheel mechanisms. Type 316 grade stainless steel is particularly effective in acidic environments. https://bmgworld.net/bmg/en/ZAR/All-Categories/Bearings/Accessories/Rolling-Elements/Balls/SB-5-8-SS316/p/SB+5-8+SS316