Assembly comprising a first part and a second part movable relative to each other in translation along a connection axis between a locked configuration and an unlocked configuration. The first part comprises one of a rail and a groove, and the second part comprises the other, the rail being configured to slide axially in the groove. The assembly comprises a ring rotatably mounted on the first part about the connection axis, the ring comprising at least one pin. The second part defines a locking ramp, a first housing and an unlocking ramp. The assembly comprises a return system for exerting a return force on the ring to a position of rest. The locking ramp and the first housing are so designed that a manual movement causes a first sliding of the pin on the locking ramp, and an automatic movement of the ring angularly in one direction between the position of rest and a first intermediate position, then an automatic displacement of the ring angularly in the opposite direction from the first intermediate position to a locking position under the action of the return system, the pin being received in the first housing, the first housing defining a first axial stop designed to block the pin axially. The unlocking ramp is so designed that a manual movement of the rotating ring in said direction from the locking position releases the pin from the first housing and causes a second sliding of the pin on the unlocking ramp, the unlocking ramp reacting axially on the pin to move the first part and the second part away from each other from the locked configuration.