Lee Valley Vise Rack Stop
http://www.consultingwoodworker.com/video_reviews We have all tried using scraps as vice spacers when clamping narrow parts. Lee Valley's Vice Rack Stop works with parts up to 4" wide and never accidentally falls out. Watch the review.
Clamping parts on one side of your vise can cause it to rack, diminishing clamping force and possibly causing damage to the mechanism. Lee Valley sent us their simple and clever Vise Rack Stop to test and review for you.