What is "handslides"

A handslide is the portion of a trombone that the player lengthens and shortens to adjust the instrument's pitch.

A handslide consists of two main parts. The first is the inner slide, consisting of two tubes or "rails" which are open at both ends and are maintained parallel to each other by a brace near one end, that is held by the player's (typically left) hand. The second is the outer slide, which is a U-shaped piece whose sides fit around the inner slide's rails. The outer slide also has a cross-brace, which is held by the player's (generally right) hand and used to move the outer slide in and out as needed.

The manufacture of handslides is one of the more precise tasks involved in instrument construction, because they must be made accurately straight and parallel over a substantial length, in order not to impede the player's playing speed and accuracy.

For further details, see under trombone.