The plugs with cold thermal range F (Fredda), have a body with thinner walls and shorter body, so they dissipate heat better and faster to the engine head. The plugs with hot thermal range C (Calda), have a body with thicker walls and longer body, so they dissipate heat better and faster to the engine head. The number of threads is the same on both types of plugs.
AFM
Which one is dissipating heat better and faster now ?
Which one has less compression ?