Didn't really know where to post this, but after some guests left and the bottom of the Jack Daniel's Single Barrel bottle is clearly visible by looking through the bottle neck, I just put it in the general discussions: Here's a link to look at some metric standardized fasteners. Click on the link, choose the DIN number, and get a dimensioned picture and the most common sizes for all metric fasteners:
DIN/ISO Specifications | Fuller Metric Parts Ltd.
BTW: A good place for individuals and businesses to order these is
McMaster-Carr
Dieter