Over the many years I was a piano technician, I came across a couple
pianos with a cast iron pin block!  I do not recall the names of the
pianos, but I do remember the information was cast into the plate.

The "pin block" was made of cast iron, with oval holes.  Regular tuning
pins were set into these oval cast iron holes.  The tension of the
string pulled the tuning pin to lock in the oval hole.  Also cast into
the plate were instructions: "Do not get any oil or grease near pins."

I did not have any difficulty tuning those pianos, and at the time I
thought it was an ingenious idea.

Bruce Clark