This 40B19 sprocket is a durable, high quality, and precision sprocket with hardened teeth. Sprockets that have hardened teeth last longer and are much more durable than those that don't. Something else that is notable about this sprocket is that it fully meets all ANSI Standards, which insures proper contact between the #40 roller chain and sprocket thus preventing premature wear or breakage. This sprocket is also black oxide coated which increases resistance to the environment and will prevent early rust build up. 40B19 sprockets with a stock bore comes with the standard 5/8" ID hole with no keyway or set screws and can be easily machine bored to custom sizes. We also offer sprockets with finished bore configurations right off the shelf from stock, and if you are needing a custom bore sprocket we the capabilities on providing those to within a fast lead time and at really great prices.