The CR1224a is the low evaporation sandwich cover used for extra high 24-deepwell MTPs. 

Other characteristics of the covers:

• The sandwich cover its function relies on the vertical force applied by a clamping system such as CR1801h or CR1700
• Autoclavable and thus reusable many times
• The cover has a blue and green filter to prevent airborne contamination
• The silicon layer is made from very durable rubber, which is free of any animal product