There are many factors that determine the appropriate rib thickness. Thick ribs often cause sink and cosmetic problems on the opposite surface of the wall to which they are attached. Factors including the material, rib thickness, surface texture, color, proximity to a gate and a variety of processing conditions determine the severity of sink.
The illustration above gives plastic part design guidelines for rib thickness for a variety of materials. These guidelines are based upon subjective observations under common conditions and pertain to the thickness at the base of the rib. Highly glossy, critical surfaces may require thinner ribs.