Sierra 18-2171 MerCruiser Engine CouplerSierra replacement round style engine coupler for all GM marine engines Except MerCruiser MR/Alpha/Bravo with Triangular, 3-bolt coupler. All Sierra aftermarket parts are manufactured to meet or exceed OEM requirements.Interchangeable with: GLM; 11500; Mallory; 9-72502; MerCruiser Stern Drive; 32492A2; 32492A3; 32492A5; 38965A1; 38965A2; 76850A2; How to Align Your Boat Engine Video