A movable subframe for a tractor-trailer includes a pair of elongated spaced-apart main members extending longitudinally relative to the tractor-trailer, at least one cross member extending between and being attached to the main members, and a retractable pin mechanism for selectively securing the position of the subframe relative to a body of the tractor-trailer. At least one of the main members includes at least one opening for receiving a pin of the retractable pin mechanism. The main member opening is formed in a shape, such as a D-shape, which reduces or minimizes distortion of the main member adjacent the top of the opening that is associated with forming of the main member.