How many parts have more than 2 faults?
SELECT COUNT ( * )  FROM  ( SELECT T1.part_name ,  T1.part_id FROM Parts AS T1 JOIN Part_Faults AS T2 ON T1.part_id   =   T2.part_id GROUP BY T1.part_id HAVING count ( * )   >  2 ) 
parts with more than 2 faults refers to counting the occurrences of faults per part and filtering where this count is greater than 2;