Abstract: The present disclosure describes selector pin for a weight stack of a weight exercise machine, and a bolt element for such a selector pin. The bolt element has two first contact points (22.1) positioned along the length of the bolt element (22) on a first side of the bolt element (22), and a second contact point (22.2) between the first contact points on a second side opposite to the first side. The first contact points (22.1) being configured to engage with the weight plate during an exercise, and the second contact point (22.2) being configured to engage with the centre selector shaft. The bolt element may further have a stress sensor configured to determine mechanical stress of the bolt element caused by forces generated by the weight plate and the selector shaft acting on the first and second contact points (22.1; 22.2) of the bolt element (22).