If you are mixing a real Colt with an Uberti gripframe, you will find the (American) Colt screw heads do not go into the Uberti countersinks, as the heads are a different diameter. I don't have them in hand to measure right now, but I recall the Uberti gripframe screws have a 5mm head and the Colt about .210 or so,, 5mm being .197. The screw threads are Colt: #8-36 and Uberti M4x0.70. .70mm translates to almost exactly 36TPI. 4mm is .157 and #8 is .164. An Italian screw will fit in a Colt, but is a hair loose and easier to strip if overtightened. An Italian frame can be chased out with an 8-36 tap to accept Colt screws, but the gripframe C'sinks would also have to be opened up or the Colt screw heads turned down a bit to fit.
Considering how soft the Italian screws are, fitting the harder Colt screw is not a bad idea.
If both the gun and the gripframe are Uberti (or Pietta) the Navy gripframe should screw right on the SAA. Note though that for some reasons, the Italian grips are a bit smaller on the Navies than on their SAA, which should not be, but is the case, so the Wood mwill probably be not interchangable.
Th.