Probably what I taught myself. To add letters I stutter the least on to words or to pronounce letters wrong to stutter less. I stutter the most on vowels and least on letters you can just flow out your mouth like h, s and f. So I would add one of those letters if the word started on a vowel. Like ”hhhexcuse me” or ”uuat time hhis it?”. Pronouncing the letters wrong still has an effect on me, I feel like I pronounce stuff wrong even though I want to pronounce them correctly.