Abstract: A spring assembly comprising a frame, a plurality of metal rails secured to the frame and a plurality of spaced spring modules secured to the rails. Each of the rails comprises a top portion and two sidewalls extending downwardly from the top portion and terminating in outwardly extending flanges. The sidewalls define a throat proximate the flanges. The spring module has at least one mounting foot comprising two opposed leg portions joined together by a connecting portion, each of the leg portions having a notch therein for engagement with a slot in the planar upper portion of the rail. The connection portion of the mounting foot is engagable with the throat defined by the sidewalls of the rail so as to inhibit lateral movement of the mounting foot within the rail.