A drain or ducting adjustment system may include a plurality of shims to elevate or space a cover from a flange or base portion of the drain or ducting. Each shim may have a recess proximate its top end to receive the cover or a higher shim and engagement means such as a lip or threading to receive the base portion or a lower shim. Shims may be of various heights. Additionally, one or more shims may allow for an angled offset between the recess and lip, in the event that the base portion of the drain or ducting is not parallel to the ultimate substrate height. Preferably, the base of the recess and lip are generally parallel to their respective end surfaces and the recess and lip are generally cylindrical such that adjacent shims may be rotationally adjusted relative to one another to achieve a desired offset angle.