The kind words about me are appreciated.
There are still screw slotting files available as I have seen them on line. I bought some at Friedrich Dick's in Deizisau, Germany many years ago. Grobet still makes them.
That said, the finer they are, the easier they break. They must be used in a holder. They are also expensive. However, if you want a tapered slot, nothing else will do.
It is best to anneal the head before you start or you will ruin the file. Start the slot with a with a fine jeweler's saw, or a hack saw blade with the kerf ground off, then finish up with the clockmaker's file.
The idea of a tapered slot is similar to a taper shank drill. The possibility of a tight fit is easier than parallel sides.
James
