Paint thickness gages measure the total thickness of the vehicle finish. It is important to accurately measure the thickness of the finish on each vehicle as the thickness of the finish will vary on each vehicle. Use a paint gage before the sanding process in order to accurately measure how much finish there is to remove before, during, and after the sanding process. Paint gages range from magnetic pull type to sophisticated electronic types, and are available from a variety of sources. The older magnetic type gages, at best have a 5 percent accuracy range and are not sensitive enough to detect removal of 0.02 mm 0.5 mil (0.0005 in) clearcoat. The newer type magnetic gages have improved accuracy ranges. Most gages are confined to checking either ferrous metal, steel, non-ferrous metal, or aluminum panel. At this time, there are no viable gages for reading film thickness on composite (SCM doors, RIM fenders) panels. The more sophisticated (ETG) electronic paint thickness gages digital type gages are able to read film thickness on both ferrous and non-ferrous metal panel. Digital ETG gages may have an accuracy range of 1 percent and include thickness standards for recalibration. The following paint thickness gages are available. Call 1-800-GM-TOOLS for information: