Replacement head gaskets for your Mercury or Mariner outboard.For 50 years Sierra has been producing parts engineered to meet or exceed the specifications of marine engine manufacturers and has gained the confidence of engine manufacturers and boat builders to a point of supplying them with OEM parts. Boaters and technicians can be assured a Sierra part will fit right the first time and restore function to OEM specifications.The Sierra Engine Parts SelectorIn addition to exhaust manifolds, we offer a wide variety of other engine parts manufactured by Sierra. To see if we have the part you need, see our Engine Parts Selector, where you can search by engine make, serial number and model or year of manufacture.Mercury Outboard Head Gasket Selection ChartSIERR#ApplicationsInterchangeModel18-3804Model 30A (S/N code 689)GLM 33880; Mallory 9-63960; Mercury Marine 27-19138M, 27-84733M, 27-19138; Yamaha Outboard 689-11181-A1-00, 689-11181-02-00491044418-3828Model 9.9C (S/N code 682) and Model 15C (S/N code 684)GLM 33890; Mallory 9-63962; Mercury Marine 27-18937M, 27-18937, 27-83899M, 27-98990M; Yamaha Outboard 6E7-11181-00-00, 6E7-11181-A1-00491046918-3861Mercury 135, 150, and XR4GLM 35850; Mallory 9-63851; Mercury Marine 27-18785-1, 27-18785T, 27-187853176313518-3862Mercury 175, 200, XR4GLM 35860; Mallory 9-63853; Mercury Marine 27-41246-1, 27-41247T01, 27-41246, 27-41247, 27-96543, 27-412462164985418-3863Mercury Model 150GLM 35880; Mallory 9-63855; Mercury Marine 27-96542-1, 27-96281T01, 27-96542, 27-96281, 27-965422176314318-3864Mercury Model 175, 200, and XR6GLM 35870; Mallory 9-63854; Mercury Marine 27-822844-1, 27-822844T05, 27-822844T04, 27-822844004, 27-822844, 27-184721, 27-8228443, 27-82284421763150