Gary, The 1 oz for 2 oz swap can be less than totally safe. The major differences, thickness and power handling, can manifest themselves in a couple of ways. If a large board contains many high-powered devices the 2 oz's may be needed to minimize plane impedance (voltage drop). The same thing applies to any board that supplies or passes-through power to a plug-in. Similarly, 2 oz`s can be a band aid for a design that has improper combinations of anti-pad size and via-to-via spacings (inadequate webs). In some rare cases, we've needed to use 2 oz copper to make up thickness on difficult/critical impedance stackups, usually in a trade-off against standard material thicknesses and narrow windows for line widths. On the other hand, a great many part numbers (primarily in the 80's) were specified with a "rubber stamp" for 2 oz copper, and this may still happen today. Good luck figuring out which case your looking at! Jeff Seeger Applied CAD