I made shims for my Ubertis and Colt 2nd/3rd gen revolvers when I substituted Ruger nipples for the Italian ones. (the Ruger nipples will not fit the Pietta) You'll need a hex wrench for the Ruger nipples. I fortunately have a lathe available. I used brass rod stock and made the shim washers, I believe .210 ID,, .310 OD and .015 thick. This brings the Ruger nipples to the proper height for the Colt hammer. If you are not substituting the nipples for slightly shorter ones as in my case, why are you shimming them? The hammer should NOT touch the nipple unless it is capped, as this will damage the nipple and hammer. If there is excessive endshake (cylinder gap) then work to reduce that so the cylinder doesn't move too far forward. If you reply with your problem and reasons for the shims, perhaps we can help you further.