We'll talk about sizing, material and special features of modern propellers to help you get started in selecting the correct wheel for your boat and intended use. There are other values, such as rake and cup that we'll go over later. Pitch is a value that describes how far a given propeller would travel through solid media in one revolution, with no slip. As an example, a 15 pitch propeller would travel 15 inches when turned one revolution in a solid block of jello. Of course, a propeller in the water experiences slip, so other factors come into play.
Pitch is an important measurement baseline when upgrading or replacing a propeller.
Diameter is the measurement from the center of the hub to the farthest outer edge of a blade times two. Increased diameter also increases blade area in most cases and this causes additional drag. Four is that shaft length and may or may not be omitted, 13.25 is the diameter and 15 is the pitch. Aluminum is very common, featuring good performance and price, and the ability to be repaired easily. Aluminum is somewhat soft and easily nicked or split, and it also flexes under load, compromising performance.