Mercruiser 43-18411A-2 Upper Gear Set – 1.50:1 Genuine OEM Mercury-Mercruiser part. Fits: MCI, R, MR, Alpha One & Gen II (s/n 0K999999 and below) (19711997) 22-20 Teeth 1.50/1.47 Ratio .Special Order Item: This product is ordered specifically for your application. To help ensure proper fitment, please confirm compatibility with your engine model using our Parts Finder & Schematics Guide before placing your order. No returns or cancellations once processed.