Pyrex: use the wire spacer, just to be on the safe side.
Flat-bottomed CorningWare Pyroceram and VISIONS: not needed, though some cooks use "heat tamer" disks on electric coil burners.
Flat-bottomed CorningWare Pyroceram and VISIONS: not needed, though some cooks use "heat tamer" disks on electric coil burners.