On Mon, 4 Dec 2017 20:05:44 +0000, Capitol wrote:

Having severe squirrel ten/1ncies, I
have a very, very large junk collection and by luck, I found that the
screw was 3/16 Whitworth and in one of my drawers was an exact
replacement for the lost screw. She then refitted the lampshade without
dropping another screw, for which I was very thankful. Junk is good!

Alteratively, you could have found a small neodymium magnet stuck to a metal
plate with a small hole, as salvaged form and old hard drive, tied two foot of
string to it (from a spool of 16 miles of fine thread), dropped it down the
sink, and hauled out the screw.

Thomas Prufer