Is there a difference between the through diameter and outer diameter of grooved pipe fittings?

Through diameter and outer diameter are a professional term used to express and describe the model of grooved pipe fittings. The specific model specifications we talk about in daily life are derived from the through diameter and outer diameter. And the names of our so-called grooved pipe fittings, such as tees, crosses, elbows, clamps, reducers, etc., are the names of the series, and have little to do with the diameter and outer diameter. So, do you know the difference between the through diameter and outer diameter of grooved pipe fittings?

The nominal pipe diameter of pipe fittings is also called the average outer diameter of pipe fittings. The nominal diameter is indicated by adding a number after the letter DN. DN nominal diameter is the general diameter of various pipes and pipe fittings (in order to make the connection size of steel pipes and pipe fittings uniform, the nominal diameter is used.) The pipes and pipe fittings of the same nominal diameter can be connected to each other, which is compatible. The nominal diameter is neither the pipe outside diameter nor the pipe inside diameter but is specified for the pipe connection. Each nominal diameter corresponds to an outer diameter, and the inner diameter value varies with the thickness of the pipe.