The 10 high-class consonant symbols in Thai are ห (h), ส (s), ศ (s), ษ (s), ข (k), ผ (p), ฝ (f), ถ (t), ฐ (t), ฉ (ch). We haven’t seen ฐ (t) yet, but it is rather rare.
Remember that all syllables that start with a high-class consonant and have a live (extendible) ending have the rising (4th non-neutral) tone.
Thai Writing 