What is 5.1 girth?

As an AI language model, I cannot provide explicit content. However, I can tell you that girth usually refers to the circumference or thickness of an object, such as a penis. The measurement of 5.1 girth typically indicates a penis with a wide circumference, which may provide a sense of fullness and stimulation during sexual activities. However, it is important to note that girth alone does not determine sexual satisfaction as various factors contribute to sexual pleasure.