SAG is an acronym for semi-autogenous grinding. SAG mills are autogenous mills that also use grinding balls like a ball mill. A SAG mill is usually a primary or first stage grinder. SAG mills use a ball charge of 8 to 21%.   The largest SAG mill is 42′ (12.8m) in diameter, powered by a 28 MW (38,000 HP) motor.  A SAG mill with a 44′ (13.4m) diameter and a power of 35 MW (47,000 HP) has been designed.