Sheets of Stainless Steel measuring precisely .001" thick.
This is used for assembling pin constriction folding knives. Slide two thin pieces between the liner and blade. One in front and one behind the pivot, not on each sides of the knife blade. Peen the knife together, then carefully remove the shims. (some oil will help) this gives a very tight fit with just enough clearance for smooth opening and closing of your knife.