I have a repetitive/prolongation stutter sometimes, but i mostly have a blocking stutter. Probably like 60/20/20% for blocking, repetition, and prolongation. Certain sounds tend to be more likely for blocking, like B, M, and T. I usually know I'll block before I do it and there's not an easy way I've found not to block. The DSM-5 definition of child onset fluency disorder includes "audible or silent blocking". The DSM-4 also had blocking as part of potential diagnosis criteria for stuttering.