Style E3 cases have a removable front lid.   Applications are heavier weight items or combinations of components that need front loading or access.  This style adapts well for multiple drawers or partitioned compartments for components. Mechanical twist catches typically two per side provide positive lid closure when case is closed.  

E4 style cases have a hinged front lid.   Hinging in typically on the left side of the case.  Applications are heavier weight items or combinations of components that need front loading or access.  This style adapts well for multiple drawers partitioned compartments for components or roll-in ramp loading of large items.  Twist catches on one side and full-length hinge on the other provide lid closure when case is closed.