Standard accuracy grades are defined by ISO 3408-3 which categorizes accuracy classes based on lead error at full length of travel (deviation) and permissible lead error along the path of travel (variation).
Standard accuracy for inch series screws is: ±.004 in/ft lead accuracy which is equal to T10 tolerance class per ISO 3408-3 classification
Standard accuracy for the metric series with OD ≤ 12mm is 52µm/300mm which is a T7 tolerance class
Standard accuracy class for metric series with OD > 12mm is 23µm/300mm with is a P5 tolerance class.