They are sold fresh, pickled or dried and flaked. There is some confusion as to whether “Pepperoncini” refers to them only when they are pickled, but the name in fact applies to the peppers in any state.
Heat level: 100 – 500 Scoville units.
Red Bell Peppers are too sweet and won’t have enough zing. On the other end of the scale, Serrano Chile Peppers would be way too hot. You want a pepper somewhere in between the two. Banana Peppers, though way bigger, might do the trick if your recipe is going to have you chop them up anyway. But if a recipe calls for 1 Pepperoncino (the singular), then only use an equivalent amount of a bigger pepper.
Literature & Lore
The “c” towards the end is pronounced “ch”.