ORIGINAL: bob27s
For a while ( a few years ago) the URNVA sent to known Jett owners included the screw. Since most of the needles are sold for "other" engines these days and the jett carb changed 5-6 years ago, he typically does not include that screw.
Problem solved is good. I think its a 3-56 x 1/2" screw ..... yes, weird size.
If it was 3-48 you could steal the 3-48 x 7/16" prop screw from a Pee Wee or Tee Dee .020.