iamburny's Y-belt clamps solve one of the problems of the Ormerod 1 design. However, another problem is that the Y belt length is only adjustable in units of the MXL belt tooth pitch, which is too large to allow proper adjustment of the tension. This is a set of 3 shims of different thickness, designed to slip under the y-belt clamps. Use them singly or in combination to get the belt tension just right.