-Sprocket Spacer. Spider Adapter. Hat Washer. No matter what you call it, you probably need it to make your sprocket fit your crank axle properly. These go on the back side of the sprocket, and are made of steel. These are not actually needed for Profile bolt-on spiders, which fit flush on a 19mm crank axle.
A. Silver–.875″ to 19mm–For 5mm thick chainwheels and spiders
B. Gold–.938″ to 19mm–For older “one piece” chainwheels
C. Black–.875″ to 19mm–For 6mm and thicker chainwheels