What does ".q" in arpabet corresponds to in English voicebanks?

I found that “.q” makes a sound that is different from others, but isn’t documented anywhere…
In Synthesizer V Studio Basic\clf-data\english-arpabet-phones.txt, there’s all the phonemes, and one of the line just says “q stop”. When i try to make Tsurumaki Maki (ENG Lite) say “.q iy”, she says something similar to hh iy (or hh ih, i can’t hear the difference)… I can’t see any word using it, and it’s clearly not a vowel. It may come from another language, for compatibility purposes, but I can’t tell what phoneme it is. If anyone know, please tell me !

EDIT : I tried other phonemes, and .q eh gives y eh, same for .q aa giving me y aa… .aa q aa give aa n aa, I’m completly at loss here.

It seems the output of q is not consistent across voice libraries. I tried with a few and got 3-4 completely different results with the exact same phonemes.

Using aa q Eleanor Forte lite treats it as a more immediate stop than cl, Maki Standard trails off into an n sound, and the English AI voices seem to trail off into a uw sound.

Based on ARPABET - Wikipedia it seems “Q” is supposed to represent a glottal stop in arpabet. Since SynthV uses cl for this instead, we can probably safely assume that at some point in early development they switched from q to cl but left it in the list for compatibility reasons. It would also explain why only Eleanor Forte lite (the oldest English voice) treats the phoneme correctly.