Holes in semiconductor processing reactor parts are sized to facilitate deposition of protective coatings, such as by chemical vapor deposition at atmospheric pressure. In some embodiments, the holes each have a flow constriction that narrows the holes in one part and that also divides the holes into one or more other portions. In some embodiments, the aspect ratios of the one or more other portions are about 15:1 or less, or about 7:1 or less, and have a cylindrical or conical cross-sectional shape. The holes are coated with a protective coating, such as a silicon carbide coating, by chemical vapor deposition, including chemical vapor deposition at atmospheric pressure.