Tuning wrench

A tuning wrench (also called a tuning lever or tuning hammer) is a specialized socket wrench used to tune string instruments, such as the piano, harp, and hammer dulcimer, that have strings wrapped around tuning pins. Other string instruments do not require a tuning wrench because their tuning pins or pegs come with handles (as with the violin), or geared tuning machines (as with the guitar or banjo).

Tuning wrench sockets may be triangular-shaped or eight-pointed star-shaped, and are found in two basic sizes: a large size for pianos, and a smaller size for most other instruments. For pianos, pins are typically square with a slight taper. There are three standard sizes known as No. 1, No. 2 and No. 3, for pins up to 6.5mm, for pins 6.5mm to 7.25mm, and for pins larger than 7.25mm. No. 2 is the most common. Wrenches are supplied with an eight-point star. Some early keyboard instruments have oblong-shaped tuning pins.

Impact piano tuning levers differ from traditional levers in that they are fitted with a weight at the end of the handle. The tuner flicks the lever with their wrist, causing the weight to do the actual work of moving the tuning pin. Tuning wrench sockets are often attached snugly to the handle with fine-gauge machine-screw threads, to provide a very firm, immobile joint; this is in contrast to the square snap-on joints found in sockets used for machinery.