Gasket seals both sides of Mercruiser center rise exhaust manifold/riser restrictor plate. Barr Mercruiser Riser Restrictor Gasket Mc47-27-41813 For Mercruiser center rise exhaust manifolds in raw water cooled applications with weep hole block off plate Sold individually - 2 required for each side of block off plate Replaces Mercruiser 27-41813, 27-41813B, 27-860233, 27-860233B, 99208A1, 863724, 863724B, 27-863724