Abstract: An insert provides for varying the inside diameter of a hole in a device such as a bowling ball. The insert has a co-axial pair of telescoping tubes joined by a thread so that the tubes may be made longer or shorter by turning one of said tubes relative to another of the tubes. The inside tube terminates at its upper end in a conical wedge shape. A flexible tube or sleeve is cemented to the outside telescoping tube to be engaged by the inside tube as it telescopes. The flexible tube has a conical wedge on its outside surface for confronting the conical wedge shaped end of the inside tube. By turning one of the tubes, the two conical wedges advance toward or retract from each other to construct or relax the diameter of the flexible tube over a continuous range extending from a fully relaxed maximum diameter hole to a fully constricted minimum diameter hole.