The minimum thickness of plates in a steel stack should be 6 mm. This is because the plates need to be thick enough to support the weight of the stack and to prevent them from buckling. If the plates are too thin, they may buckle under the weight of the stack and cause the stack to collapse.
Option A: 4 mm is too thin. The plates need to be thick enough to support the weight of the stack and to prevent them from buckling. If the plates are too thin, they may buckle under the weight of the stack and cause the stack to collapse.
Option B: 5 mm is not thick enough. The plates need to be thick enough to support the weight of the stack and to prevent them from buckling. If the plates are too thin, they may buckle under the weight of the stack and cause the stack to collapse.
Option C: 6 mm is the minimum thickness required. The plates need to be thick enough to support the weight of the stack and to prevent them from buckling. If the plates are too thin, they may buckle under the weight of the stack and cause the stack to collapse.
Option D: 8 mm is too thick. The plates do not need to be this thick to support the weight of the stack and to prevent them from buckling. Using thicker plates will only increase the cost of the stack without providing any additional benefit.