A method of assembling a spring inside of a tube includes providing a coil spring and a tube having a first retaining structure at a first end of the tube. The method includes positioning a rod in the tube. The spring is positioned in the tube, and a second retaining structure is attached to the rod with the spring positioned between the first and second retaining structures. A force is applied to the spring, and the second retaining structure is fixed at a position wherein the spring provides a desired preload.

Chair comprising a support structure provided with a first housing seat having a first non-circular opening, and with a support element, which is mechanically connected to the support structure and is provided with a second housing seat, which is aligned and communicating with the first housing seat. The chair also comprises a removable connection system having a locking pin provided with a non-circular head, which engages the first housing seat and the second housing seat and is rotatable between a release position, in which it releases the support element from the support structure, and a constraint position, in which the support element is constrained to the support structure. The locking pin comprises an elastic retention element which is elastically engaged in a first retention recess of the first housing seat when the locking pin is in the constraint position, in order to retain the locking pin therein.

The invention relates to a synchronizing mechanism for a chair comprising a base part which defines a rotational axis, a backrest support for supporting a backrest and a seat support for supporting a seat. The backrest support is pivotably supported on the base part about a first pivot, and the seat support is pivotably supported on the backrest support about a second pivot. The first pivot of the backrest support is fixed relative to the base part and the second pivot of the seat support is movable relative to the base part. In a basic position, the second pivot is in a lower basic position and the seat support rests against a support structure. In an upper end position, the movable second pivot is moved substantially vertically into an upper end position and the seat support is arranged at a distance to the support structure.

A chair that provides movement of a seat about an axis of rotation above the seat plane with the seat having a sensor in communication with a computer system that tracks movement. The seat may be simultaneously pivotable about a second axis of rotation defining a range of motion for the seat about the two axes. An actuation system in communication with the computer system can move the seat to desired positions and/or prevent the seat from being positioned at certain locations within the range of motion. The computer system may also include an application that can promote user movement within the seat and allow movement of the seat to be used for gaming, health monitoring and treatment, activity tracking, and the like. The chair may include a mechanism that has one or more glides operably received in curved structures to provide the movement about the axes.