{"product_id":"sierra-18-7121-o-ring-for-omc-cobra-mercruiser-stern-drive-replaces-oem-308621-3-100-i-d","title":"Sierra 18-7121 O-Ring, 3.100 Inch ID, Replaces Mercury 25-35029, for OMC and Mercruiser Stern Drives","description":"\u003cp\u003eThe Sierra 18-7121 is a rubber O-ring built for OMC, Mercury, and Mercruiser outboards and stern drives. It has a 3.100 inch (78.7 mm) inside diameter and a 0.135 inch (3.4 mm) width, and is sold as one O-ring per package. The compound is black rubber, sized to seal against fluid loss and contamination at stern drive and outboard housing joints where a properly dimensioned O-ring is required for a tight fit. Sierra manufactures this part to meet or exceed the specifications of the original equipment part it replaces, making it a direct equivalent for OMC Stern Drive, Mercury Marine, and Mercruiser Stern Drive applications, as well as compatible with Mallory and GLM cross-reference numbers. Because O-rings harden and lose sealing ability with age and heat cycling, this is a common maintenance replacement item to keep on hand for stern drive service or rebuild work. Its simple, small-parts design means it installs by hand into the mating groove during reassembly, with no special tools required.\u003c\/p\u003e\u003ch3\u003eSpecifications\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Sierra\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number:\u003c\/strong\u003e 18-7121\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInside Diameter:\u003c\/strong\u003e 3.100 inches (78.7 mm)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWidth:\u003c\/strong\u003e 0.135 inches (3.4 mm)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Rubber\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eColor:\u003c\/strong\u003e Black\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUnit Count:\u003c\/strong\u003e 1 O-ring per package\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.01 pounds\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUPC:\u003c\/strong\u003e 030999321398\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eOMC, Mercury, and Mercruiser outboards and stern drives\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eReplaces (OEM)\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003eMallory 9-76651\u003c\/li\u003e\n\u003cli\u003eGLM 82350\u003c\/li\u003e\n\u003cli\u003eMercury Marine 25-35029\u003c\/li\u003e\n\u003cli\u003eOMC Stern Drive 308621\u003c\/li\u003e\n\u003cli\u003eMercruiser Stern Drive 25-35029\u003c\/li\u003e\n\u003cli\u003eMercruiser Stern Drive 27-882613\u003c\/li\u003e\n\u003cli\u003eMercruiser Stern Drive 802231\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eWhat is the inside diameter of the Sierra 18-7121 O-ring?\u003c\/strong\u003e The Sierra 18-7121 has a 3.100 inch (78.7 mm) inside diameter and a 0.135 inch (3.4 mm) width.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhich stern drives and outboards does this O-ring fit?\u003c\/strong\u003e The 18-7121 is designed for use with OMC, Mercury, and Mercruiser outboards and stern drives.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the Sierra 18-7121 the same as OMC part 308621?\u003c\/strong\u003e Yes, the Sierra 18-7121 is interchangeable with OMC Stern Drive part number 308621, along with several other OEM equivalents.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat OEM part numbers does the 18-7121 replace?\u003c\/strong\u003e It replaces Mallory 9-76651, GLM 82350, Mercury Marine 25-35029, OMC Stern Drive 308621, and Mercruiser Stern Drive 25-35029, 27-882613, and 802231.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow many O-rings come in one package?\u003c\/strong\u003e Each package of the Sierra 18-7121 contains one O-ring.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat material is the Sierra 18-7121 O-ring made from?\u003c\/strong\u003e It is made from black rubber, sized for a durable seal in stern drive and outboard housing applications.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much does the Sierra 18-7121 O-ring weigh?\u003c\/strong\u003e The Sierra 18-7121 O-ring weighs 0.01 pounds.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the Sierra 18-7121 a genuine OEM part or aftermarket?\u003c\/strong\u003e The 18-7121 is a Sierra-manufactured replacement part built to meet or exceed the original equipment part it replaces, rather than a factory OEM part.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDo I need any special tools to install the 18-7121 O-ring?\u003c\/strong\u003e No special tools are needed; the 18-7121 is a small O-ring that fits into its mating groove by hand during reassembly.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhen should the 18-7121 O-ring be replaced?\u003c\/strong\u003e Because O-rings harden and lose their sealing ability over time and with heat exposure, the 18-7121 should be replaced any time the sealed joint is disassembled for service or if leakage is found.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the UPC for the Sierra 18-7121?\u003c\/strong\u003e The Sierra 18-7121 O-ring carries UPC 030999321398.\u003c\/p\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":48988364210395,"sku":"SIE-18-7121","price":2.14,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0839\/7586\/4539\/files\/18-7121__59213.1722379412.500.750.jpg?v=1785188657","url":"https:\/\/www.goodvibesmarina.com\/products\/sierra-18-7121-o-ring-for-omc-cobra-mercruiser-stern-drive-replaces-oem-308621-3-100-i-d","provider":"Good Vibes Marina","version":"1.0","type":"link"}