Sierra International 18-0549 Plug Off Cap The Sierra 18-0549 Plug Off Cap is interchangeable with the following: GLM 22290, Evinrude/Johnson 909829, 3852476, Mallory 9-42720, Volvo Penta 3852476. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Plug Off Cap ID: 1" or 25.4mm Sierra part number: 18-0549 Interchangeable with the following: GLM 22290, Evinrude/Johnson 909829, 3852476, Mallory 9-42720, Volvo Penta 3852476