The pinblock (or the wrestplank as it is sometimes called) is the block of wood that is behind the plate of the piano and holds the tuning pins tightly. It is one of the most important parts of the piano. Its job is to grip the tunning pins so that piano does not go out of tune. In most grand pianos, the pinblock is not visible, but is directly underneath the tunning pin portion of the plate.It must be built strong enough to withstand the cumulative force of all of the strings pulling on the tuning pins.
Pinblocks do not always have to be replaced. Frequently a pinblock can be reused an oversized pin can be installed originally pins are size 1 or 2, the pins can go up to size 7. A lot depends on the age and condition of the pinblock and the piano itself. As a piano ages it often suffers from extremes in temperature and humidity, which can cause the tuning pins to become loose. This happens because the wood of the pinblock shrinks and the size of the hole into which the tuning pin is installed expands.
If only one or two tuning pins are loose, an appropriate repair is to remove the tuning pin and to replace it with a larger sized tuning pin, or to install a shim in the tuning pin hole.
Either of these repairs will provide enough friction to allow the piano to be tuned again. Experienced craftsmen set the exact location of the pin and tuning-pins, as the cuts of the pin are all handmade.
The pin and its position are measured for each piano individually with special tools.