When I ordered witch hat knobs for my AlFemBic, it came with the correct hex wrench for the set screws. However, I have misplaced the wrench! Anyone know the proper size so I can buy a new one?

The page you link to says 1/16 inch allen key for installation. Happy Friday.

If you can't find a 1/16th allen key, you could probably make due with a pointy, rusty screwdriver and a pair of garden shears.  Either that, or just pull really hard.  

Oops - I didn't read carefully enough! Thanks!
 
I'm not gonna just pull really hard because that already happened once!