Horstman axle sprockets are USA made have been number one in karting for over twenty-five years for numerous reasons.  They are made from .160" thick 7075-T6 aluminum alloy for strength and toughness.  They have lightening holes to reduce unwanted rotating weight.  They are hobbed for accuracy and anodized red for lasting protection. The center hole clears the industry standard 4 9/16" hub register, as well as metric standard. Sprockets are .306" pitch #219 chain. They are available (Special Order) in the 2 piece style for mounting inside the frame rails.  Look for the color "RED" and the name Horstman, don't accept cheap Chinese imitations.