anything to "occupy" some of the spacing ( gap) of the bottom (flat) of any dovetail and the bottom "flat" of the sight body itself......this pushes up against the dovetails slot ,front and back...this being said yes a thin shim can work but , if it shifts and moves as you are driving in the sight, it can AND WILL come out and show on the other side.......so as often noted, just a few divots with a punch and the slide sitting on a HARD , level surface, stake just a few holes, divots, punch marks, whatever you want to call them, its called "raising metal", just enough to "tighten" up the gap (looseness) and yes, if you take and move the sight off and on and off and on, you are going to loosen it up again,,,,,those punch marks do flatten off with going on and off...........no need to use Loctite or some such, as the first time you try and drift the sight, you break the integrety of the Loctites "bond".....and yes recoil can do that also............same goes for "pistol whipping" 8) :roll: :wink: