Strings (tennis)
The material used in tennis string can significantly affect a player's performance, and even health. Several materials are used to make tennis strings. They vary in terms of elasticity, durability, rebound efficiency, tension holding capability, and manufacturing cost, among other considerations.
Tuning wrench
Tuning wrench sockets may be square-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, there are some gradations of size, and several lengths are generally available, and unlike machine-screw sockets which have no taper, piano sockets have a slight taper, to fit tapered 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 his or her 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.