On Wed, 28 Sep 2011 13:22:39 -0400, Alex Michael wrote:

Can somebody tell me what this type of screw is called? It came from
a Hard Drive caddie.The screw fits into a slot so the Hard Disk doesn't
move around,that is why the thread don't go all the way.Thanx

http://www.imagebam.com/image/73aa09151484111

Shoulder screw.

Right column:
http://www.accuratescrew.com/Other-Screws.aspx