An apparatus including a guide track member for a first part, a guide pin for a second part and a first biaser. The first and second parts being for a portable electronic device and the guide track member including first and second guide track portions. The apparatus is configured such that the guide pm travels within the respective guide track first and second portions to provide respective first and second bistable configurations of the apparatus in which the first and second parts are held in relative positions to one another. The first biaser is configured to apply a lateral force to the guide pin to cause it to travel along the first portion of the guide track when moving from the first bistable configuration to the second bistable configuration and to apply a lateral force to the guide pin to cause it to travel along the second portion of the guide track when moving from the second bistable configuration to the first bistable configuration. The transition between the bistable configurations is provided by relative movement of the first and second parts in the same direction.