Several different types of diffuser rings can be used with gas and electric stoves. However, a ceramic stovetop needs a particular type of diffuser ring that can also be used on other types of stoves.
At the cheaper end of the scale is the Norpo 144, which is suitable for gas and electric stoves, but cannot be used on ceramic stovetops. Because it is made of tin, it cannot be put in the dishwasher either.
A diffuser ring helps spread the heat evenly across a pan, ensuring that there are no hot spots that encourage food to burn or stick to the pan.