According to Duchossoir, the threaded saddles were used from late 1958 until early 1968. At that time the threaded saddle were replaced with grooved steel saddles. Earlier steel saddles from the '50s did not have the grooves.
I went back and see that your saddles don't have the grooves. I suppose there's always the possibility that a Fender assembler came across an old set of saddles in the back of the drawer and put them in.
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Jack's Disclaimer: When I say something.... always ask yourself ..... "What the hell does he know?" _
Guys - learn to disable the flash on your digital cameras.