Our 1/8" (3.175mm) Tungsten Carbide balls are recommended in diffs that don't have prepped rings (sanding the rings lightly on a granite counter top with some 600 grit sandpaper or from a company that does this already). Stock rings typically have a polished finish which can be too slippery for ceramic balls if you don't have patience to set the diff correctly. Our tungsten carbide ball is smoother than the stock steel balls but not as smooth as a ceramic ball, this slight imperfection allows the tungsten carbide ball to perform on the polished rings and allows for a wider tuning window.
These 1/8" (3.175mm) tungsten carbide diff balls are commonly used in the spur gear of 1/10th and 1/12th scale cars. Please check your manual for the correct size.