A slider has a board that has a bottom surface, a top surface, a front edge, a rear edge and two side edges. A single recessed longitudinal channel is provided in the bottom surface and extends continuously from the front edge to the rear edge in a manner that divides the bottom surface into two separate longitudinal sections on either side of the channel. The channel is defined by two opposing curved longitudinal surfaces that configure the channel in a manner where the channel is wider at the front edge and the rear edge than at the center of the channel