Abstract: An apparatus including a first part, a second part, a plurality of spaced apertures in the first part and a plurality of holding devices for holding the first part against the second part. The plurality of apertures are each selectively sized so a first of the apertures forms a close clearance fit with one of the holding devices on at least one diameter of the first aperture. A second of the apertures forms an equally close clearance fit, on one of its diameters, with a second of the holding devices, but forms a looser clearance fit with the second holding device on a second diameter thereof, which generally parallels a line between the first and second apertures. The remainder of the plurality of apertures each form a substantially looser fit with an associated holding device than is formed by either of said close clearance fits.