The term "ATA case" is frequently used to describe cases that resemble those that comply with ATA Specification 300 category I or II, but have not been certified by the independent testing defined in ATA Specification 300. Category I and II cases are required to be tested both as a pre-production prototype and as a sample selected from the first production lot. Tests include stackability, drop or impact, water resistance, vibration (category I only), and penetration (category I only). Of these, the drop test, stackability, and vibration tests are probably the most severe. For cases under gross (loaded) the drop test requires 160 face drops from , 80 edge drops from , and 40 corner drops from 36 inches. The face drop distance is reduced to up to , , or more. Category II cases are dropped one-tenth as many times from and at 50 pounds, and proportionally for heavier cases. The stackability test requires every case face over to support centered on of the face for 24 hours. The vibration test searches for the four strongest resonances between 5 and 50 Hz, and then tests each at for 2 hours on each principal axis. The penetration test is a 6-kilogram steel bar 3.2 centimeters in diameter with a hemispherical end dropped 0.5 meters on the weakest point. For all tests no degradation or functional damage is allowed.