O-ring 04150, Silicone Silicone o-ring commonly used throughout La San Marco espresso machines for boiler, valve, and fitting seals. SPECIFICATIONS Part #: 04150 Material: Silicone Thickness: 3.53 mm Internal diameter: 37.69 mm COMPATIBILITY Fits: Applications requiring a 04150-size silicone o-ring (3.53 mm thick, 37.69 mm ID), cross-check against your machine's parts diagram INSTALLATION Simple DIY replacement.