Where should I measure the deposit thickness?

Thickness of electrodeposited coatings varies from point to point on the surfaces of a product. The thickness is less in interior corners and holes. Such surfaces are normally exempt from the thickness requirement. If the full thickness is required on these surfaces, the electroplater will have to use special techniques that probably will increase the cost of the process.

Because of deposit thickness variability, it is necessary to identify the key operational area on the coated article where the deposit must function. These locations are defined as the functional significant surfaces.   Functional significant surfaces are best defined as a portion of the surface of a coated article at which the coating is required to meet all of the requirements of the coating specification for that article; significant surfaces are usually those that are essential to the serviceability or function of the article, or that can be a source of corrosion products or tarnish films that interfere with the function or desirable appearance of the article; significant surfaces shall be indicated on the drawings of the parts or by the provision of suitably marked samples.

For applications in precious metals, it is critical to define the functional significant surfaces of the component where the application of the deposit is important to the part function/design.  Often times, if surfaces that are functionally critical are clearly identified on the part print, the overall gold or silver usage on the product can be reduced.  This can often result in significant cost savings vs. applications where no such distinction is made.