A binding structure for binding a bundle of sheets and that includes a base and a pair of opposed position legs that are integrally formed with and extend from respective sides of the base. The pair of legs and base together defines a retention area in which the bundle of sheets is held. The pair of legs is constructed and arranged with a resilient bias toward each other, but separable to enable the bundle of sheets to be held therebetween under a biasing force. The legs each have at least one inwardly directed rib arranged for contact with opposed sides of the bundle of sheets, and a thermal adhesive layer is disposed on the base and upon which the bundle of sheets rests, to be later formed in a thermal binding machine.