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.