83mm (MP83) vs. 78mm (MP78) mounting pitch, which kit do I need?

Depending on the model, most Noctua CPU coolers feature a mounting pitch (distance between the spring-loaded mounting screws) of either 83mm (coolers with two-piece fastening brackets) or 78mm (coolers with single-piece fastening brackets). Coolers with 83mm mounting pitch require the MP83 kit whereas coolers with 78mm mounting pitch require the MP78 version.