Hi Gray,
Outside of 'V' type screw measures dia 2.25mm but unable to measure inside as vernier blades too thick.
I think I would try a 2mm drill to open the hole, take a spare 'V' type screw and cut a slot in the thread each side and use this screw as a tap but gently and back off regularly.
I don't know what the thread is and doubt that the Chinese will tell us. I have tried the the screw in a 2.2mm and 2.5mm die but didn't want to go so assume not metric as we know it.
Hope this helps.
Alec
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