Dear stutterer, ​ I am a stutterer myself who was able to overcome the vast majority of his stutter due to speech therapy in Germany. Unfortunately, I am not a speech language pathologist and don't know everything about muscle tension and so on. But, I can share some insights I got from my own treamtent with you. Like you, my only stutter symptom is the block. No prolongation or repetition. The bllock occurs when we got no "Atemstütze" as my therapist put it. We need to be able to breath in enough air to pump up our "Zwerchfell" (I guess its diaphragm in English). Because, if you got enough air and open your mouth correctly you shpuld not be able to block (Why this is the case I have to ask my therapist.) You can try to strengthen your ability to breath and your volume by a.) learning a breathing pattern where you breath in your diaphragm and not your chest and by b.) speaking in staccato (which means in syllables). Thereby, you will see that you are synchronizing the new breathing pattern with your articulation. Also, by speaking in staccato and "overforming the words" as you are speaking slower you give the muscles involved in forming the sounds enough time to form them.) Maybe this can help. Unfortunately, I cant dive into distinct exercises for specific sounds as I am not a speech language pathologist myself and dont want to share information that Idont know whether it is true. Currently, I try to get into contact with other stutterers on discord to speak to them as I am pondering with the idea of becoming a speech language pythologist myself. Maybe you want to message me to schedule a time to speak (no charge involved, I am not taking money, I did not study this, I just want to talk. I am just writing this to make my intentions clear). Maybe I can't help you, maybe my experience is at least slightly helpful. ​ Best regards!!