Coupling system for chair parts

A chair, comprising

• a chair base assembly,
• a chair seat,
• a chair seat support structure coupling the chair seat to the chair base assembly,
• a backrest or an armrest provided with a connecting member, and
• a coupling system, comprising a receiving support to be provided at one of the connecting member and the chair seat support structure, an insert terminal to be provided at the other one of the connecting member and the chair seat support structure, wherein the insert terminal comprises a first pin and a second pin, wherein, in a use position of the chair with the chair part coupled to the chair seat support structure via the coupling system, the first pin and the second pin extend horizontally from a vertical surface of the insert terminal, wherein the receiving support provides a longitudinal support guide with a stop at a first end of the longitudinal support guide, and a pin insertion opening and a recess at a second end of the longitudinal support guide, wherein the pin insertion opening is configured to allow insertion of the first pin and of the second pin, and
• wherein a distance between the stop and the recess is essentially the same as a distance between the first pin and the second pin such that the second pin is insertable in the recess when the first pin abuts the stop.