EXACT SPECIFICATIONS: This is a 3-3/16 inch diameter FLAT (smooth) pulley. It sits securely against the back side of the serpentine belt to maintain proper routing and tension to critical components like your seawater pump and alternator. DIRECT OEM REPLACEMENT: Replaces Mercury, MerCruiser, and Quicksilver OEM part numbers 8M6500024, 865598, and 818382. BROAD COMPATIBILITY: Designed to fit 1999 and newer Mercury / MerCruiser Alpha and Bravo sterndrive and inboard engines. Compatible with V6 and V8 block sizes including 4.3L, 5.0L, 5.7L (350 MAG), 6.2L (377 MAG), 8.1L (496 MAG), and 8.2L MAG. MARINE-GRADE DURABILITY: Constructed from high-strength, heat-resistant thermal resin to withstand extreme engine bay temperatures and harsh marine environments. Features a permanently molded-in bearing for quiet, wobble-free operation and maximum longevity. BUYER VERIFICATION WARNING: Please confirm you need the SMOOTH idler pulley before purchasing. These engines also utilize a larger 4-1/4" grooved pulley in the same belt system. Keep Your Marine Engine Running Smoothly Don't let a worn-out serpentine belt pulley ruin your day on the water. This premium Replacement Smooth Idler Pulley is engineered to meet or exceed OEM specifications for Mercury and MerCruiser marine engines, delivering reliable performance and perfect belt alignment. Constructed from heavy-duty thermal resin with a precision-molded internal bearing, this 3-3/16" flat pulley resists the high heat and heavy vibrations produced by powerful inboard and sterndrive engines. Replaces OEM Part Numbers: 8M6500024, 865598, 818382 Compatibility: Fits 1999 & newer Mercury / MerCruiser Alpha & Bravo sterndrive and inboard engines, including: 4.3L V6 (Alpha & Bravo) 5.0L V8 (Alpha, Bravo & MPI) 5.7L V8 / 350 MAG (Alpha, Bravo, MPI & Horizon) 6.2L V8 / 377 MAG (Bravo, MPI & Horizon) 8.1L V8 / 496 MAG (Bravo & H.O.) 8.2L V8 MAG (Bravo & H.O.) Custom/Stroker Blocks (357 Scorpion, 383 MAG) Important Installation Note: This listing is for the FLAT/SMOOTH pulley only. MerCruiser serpentine systems often use both a smooth pulley and a larger 4-1/4" grooved pulley. Please verify your specific part requirement visually or via your engine's parts diagram before ordering.