Slotted box holds qty 25 MF-25 membrane frames.  The round frame supports two membranes that firmly holds your specimen between them.  Frames open (blue hinge) to allow placement of your object, and snap together (red latch).  (Frames are NOT boxes.) Frames available in collars of  8 mm depth.   

Frame diameter  ~  75mm 
Membrane diameter = 60 mm.