SEI SE221 Lower Unit for Mercury 3.0L V6 2-Stroke 1.75:1 RatioThe SEI SE221 is an aftermarket replacement lower unit for select Mercury 3.0L V6 two-stroke outboards in 200300 HP applications. Featuring a 1.75:1 gear ratio, this standard gearcase configuration uses a 13-spline driveshaft, 15-spline propeller shaft, and 4.88″ torpedo housing. Choose from 20″, 25″, or 30″ shaft-length options to match your engine application.This item is subject to a 20% restocking fee.Year, serial number, and horsepower are required to process your order. Please contact us with this information after placing your order. Processing will be delayed until this information is received.FeaturesAftermarket replacement for select Mercury 3.0L V6 two-stroke lower unitsFor compatible 200300 HP applications1.75:1 gear ratio13-spline driveshaft and 15-spline propeller shaft4.88″ torpedo housingAvailable for 20″, 25″, and 30″ shaft lengthsShaft Length and Replacement References20″: SEI 90-221-A20; replaces OE numbers 880686T29 and 880686A4325″: SEI 90-221-A25; replaces OE numbers 880686T33, 880686A44, and 842004T2630″: SEI 90-221-A30; replaces OE numbers 880686T34, 880686A51, and 842004T28Fitment RequirementsConfirm your engine serial number, existing gear ratio, shaft-length designation, spline counts, and gearcase type before ordering. Horsepower alone does not establish compatibility.This SE221 configuration replaces the standard-style gearcase, which may also be referred to as a Fleet Master. It does not replace Torque Master, Torque Master 2, or Sport Master gearcases.These versions use a 13-spline driveshaft for the listed two-stroke applications. They should not be substituted for the 20-spline SE221 versions used in four-stroke applications.