Dune,
Most of the screws are made from brass, the screw part that is. The handle area can be different although I think many are aluminum. Haven't much heard of the brass wearing out. There are some excellent choices here on this site. I prefer the CRF's only fuel screw.
http://www.crfsonly.com/catalog/product ... ts_id/1333
The JD kit is excellent. Just follow the directions and your bike should be good to go. JD has excellent support so if you have any questions email or call.
Nice pic
Luke