The measurements given in the catalog and on-line are the diameter of the dial including the bezel from (A) edge to (B) edge. When measuring for opening, there is approximately 1/8" from the nail holes in the dial to the outer edge of the bezel ring. Order your dial about 1/2" larger than the opening in your case (C). This will keep the dial from sliding into the hole and also allow sufficient material to attach the dial to your clock case.