A rotatable spring biased clamp for mounting on the platform of a bicycle rack pivots about the perpendicularly extending lugs ends of its legs. Each leg end is emgaged with a torsion spring that provides both a rotational force to the clamp, to hold objects on the platform, and a vertically bias on the lug ends, to hold them in place against the platform of a bicycle rack during use. The legs are elastically deformable toward each other, and coil type torsion springs have hook shaped tangs; the clamp is thus easily mounted on or removed from a rack platform without tools.