Mason & Hamlin experimented with a tuning method that did away with the tuning pin held by friction in a wooden pin block, and substituted a system based on metal machine threads. Adjustment of pitch was accomplished by turning a square-headed bolt with a wrench, using far less force than required for a standard tuning pin. Creating a stable tuning was somewhat of a challenge when a piano aged, and friction developed between the string and bearing points. The general advice was always to approach pitch from below. The system was applied to grand pianos as well as uprights.
This was not a new invention, as Sébastien Érard had invented a similar system in the 1820s.