Standard race materials are low carbon, heat treated alloy or stainless steel. Balls are precision ground alloy or stainless steel. Metal on metal race units can be relubricated through an annular groove in the outer race with two inter connecting holes positioned at 180 degrees, while a self lubricating PTEE metal interface may also be optional specified in many seried. Inch or imperial sizes range from 3/16 inch through 6 inch bore, metrics from 3 through 160mm.