On a sprocket, what do the letters A, B, C refer to?

The letters A, B, and C on a sprocket refer to the hub class, which is essential for identifying the design and construction of the sprocket's hub. The hub is the central part of the sprocket where it attaches to the shaft, and the hub class specification determines how the sprocket interfaces with various chain types and the overall alignment within the power transmission system. Understanding the hub class is crucial for ensuring proper fit and function in mechanical applications.

The other options pertain to different aspects of sprockets and chains, but they do not specifically correlate to the letters A, B, and C. Tooth size refers to the dimensions of the individual sprocket teeth, which are critical for engaging the chain effectively. Pitch represents the distance between corresponding points on adjacent teeth, which is crucial for matching the sprocket to the right chain. Type of chain indicates the specific design characteristics of the chain used, and while this is important for selecting compatible components, it does not relate directly to the hub classification marked by A, B, and C.