On Saturday, February 3, 2018 at 11:56:41 PM UTC-5, Charles Longley wrote:
The empty package says 4 mm and a 4 mm screw from the hardware store screws in perfectly. Sooo I am guessing it’s a 4 mm screw....

Well, in that case, let us know what standard that strange screw is when you find it.
Uli
'AS'