Homemade Sausage Making

Quick question. I have been making fresh Italian sausage and it taste very good. My nephew was also here and he likes more heat. My question is what do most people use to create more heat for hot italian sausage. Is it just more red pepper flakes or something else? Let me know. Thanks.

I just use ground cayenne and more black pepper to make it hotter.

Mostly I used generic hot pepper flakes and Hungarian hot paprika. I have also tried Szechuan peppers (not a true pepper) and have recently bought a package of Calabrian peppers. Haven't tried them yet, but I thought that if I am going to make Italian sausage, then I should also use Italian peppers.