by JimN » 28 Sep 2013, 14:41
Just to add to and support what Alan Bakewell says, I have two Fender USA 1962 Vintage Reissue Strats (made in the 1980s). They are equipped with original design solid steel trem blocks and the arm/thread fit is perfect: no sloppiness, no play, no rattles, no clunks through the pickups and a perfect smooth feel to the operation.
The Callaham blocks, to my knowledge, are just as good, if not better.
It is cheaper, cast alloy, blocks, including some of those used by Fender USA in the 70s and very early 1980s, which cause the problems. The metal is miles more susceptible to wear and really isn't suitable for threads which have to bear stress.
I don't know how much difference there is between steel and alloy blocks in sound (somewhat less, I suspect, than the makers of boutique replacement steel blocks claim), but in terms of the mechanical coupling between the bridge and the arm, alloy threaded blocks are a non-starter for longevity. They may be a bit better than useless with a pop-in interface, but even then, the material cannot provide a secure thread for the little grub screw which is necessary for tensioning the arm fit.
Alloy: get rid.
Steel: just the thing.