I’m no expert but from experience I think there are 3. -Repetition: r-r-r-repetition / repe-repetition -Prolongation: pppppprolongation -Silent blocks: you freeze without making any sound or noise. Words don’t come out. And of course, these 3 can have a lot of variations and can be combined. Some stutterers also add some sounds or fillers before each word like uh, uhm, er, ts… etc. I personally prolong words with initial silent blocks.