Proper Nonagon Sprocket This is a revised version of the classic Magnalite sprocket adapted to fit all cranks (apart from non-socketdrive Odyssey cranks). Fits straight on to Socketdrive Odyssey Thunderbolt cranks with no spacers. CNC 7075 alloy. Sizes: 25t or 28t. Weight: 58 grams for 25t. 68 grams for 28t