Abstract: A chair, particularly an office chair, comprises a chair column, a seat lower frame supported on the chair colunm in a height-adjustable manner and rotatable relative to a vertical axis, a seat support supported on the seat lower frame turnably about a horizontal axis, a backrest support supported on the seat lower frame turnably about a horizontal axis, at least one spring with adjustable tensioning and supported on the seat lower frame and the backrest support, an adjustable abutment provided for the pressure spring, a control curve against which the adjustable abutment abuts, and an adjusting element arranged to displace the control curve.

Abstract: In a gas pressure spring for a chair, a locking device is provided, which includes a safety sleeve formed of two semi-circular halves which are clamped on an outer tube of the gas pressure spring by clamping bolts. The outer tube is formed with an end portion of a reduced diameter and a transition zone. The two halves of the safety sleeve are formed each with an inner collar matching the transition zone of the outer tube. One of the halves is formed with a through opening for passing a height-adjusting lever towards the outer tube.