These sounds are pronounced as the voiceless-stops with an “h”-like puff of air after it. English does not distinguish between aspirated and unaspirated voiceless stops. English speakers tend to aspirate stops which stand alone at the beginning of words: “pen”, “ten”, “ken”; if you put your hand in front of your mouth, you can feel the puff of air. English speakers tend not aspirate stops at the ends of words: “sip”, “sit”, “sick”. Primitive Adûnaic, like Khuzdul and Primitive Elvish, did distinguish between aspirated and unaspirated voiceless stops, and they could appear in any place in a word, beginning or end. In Classical Adûnaic, these sounds mostly developed into voiceless spirants, except for ✶[cʰ] which early on became [s].

For brevity, the discussions here generally refer to “voiceless aspirated stops” as simply “aspirates”.