Fixed and opening dimensions.
F: Solid tool dimensions. This can achieve tighter tolerances on the finished part compared to "C".
C: Open tool dimensions, they have a wider tolerance and therefore cannot achieve the same tolerances as "F"
See drawing of tool for explanation of F and C
M1: This tolerance class is only used for precision molded parts. This normally requires one cavity tools, custom rubber mixtures. Means high detail costs.
M2: Used for moulded parts with high demands. In many cases, the demands on materials and process is like, M1 tolerances.
M3: Used for molding parts with normal tolerance requirements.
M4: Use for details where the dimensions are not as critical.