Abstract: A fastening mechanism of hollow parallelepiped comprises two ribs on an underside of a top, and a rail on an inner wall of either side. An expansion slot includes a bifurcation at one end with a well defined therebetween. Either branch of the bifurcation includes a top recessed first catch distal from one end, a top recessed second catch proximate one end, and an upright latch on an inner wall. Responsive to inserting the connector of a card into the expansion slot with a projection at one end of the connector entered the well and being fastened by the latches, push the mechanism toward the bifurcation for moving the ribs to pass the second catches to engage with the first catches as the branches slid into the mechanism to matingly engage with the rails.