The AI logo thumb screws that I have measure 21.4MM. The most recent ones that I received from Sporting Services measure 20MM and the work fine. They are flush against the skins. Keep in mind that there is a barrel above the threads on the McMaster-Carr that is 10MM. The hole on my AT skins measured 9.97MM. So you should be able to open up the hole on the skins if needed. It may work out better to shorten the threads and have the barrel body recess into the AT skins.These are long enough to contact the studs in the cheek piece? I ordered some other ones and the 20mm weren’t long enough. I trimmed 25mm ones to make them work
Talking the AT thumbhole