Agree with the above post.
For electric stoves, there is also an electric "burner" accessory element that is raised up (replaces a standard plug-in coil-type element). It serves a similar puropose. It's for large stock pots and canners, etc. that would hang over a standard 8" element. (That, I know for a fact, is roughly 20cm). Prevents heat damage to cootop surface.