Slide this Mercury Sleeve-Prop Bore (23-8M0214998) over the prop‐shaft splines and give your outboard the snug, vibration-free fit it deserves. Molded from Mercury's impact-modified polymer, the sleeve fills the minute gap between hub and bore on Alpha, Bravo, and late-model FourStroke drives-so every ounce of thrust pushes the boat, not the shaft.. What this little sleeve really does. Centers the prop dead-true, cutting rattle and cavitation at idle and wide-open throttle alike.. Absorbs shock loads with a self-lubricating shell that won't crack under hard reverse or sudden throttle punches.. Protects splines and seals by keeping exhaust gases out of the hub cavity and corrosive water away from the shaft.. Drops in by hand during any prop change-no tools, no sealant, no guessing on fit.. The result? Smoother hole-shots, cleaner shifting, and longer life for that pricey stainless wheel. Keep a spare in the tackle box; the five-minute swap pays for itself every time you feel the prop lo