1.5 inch Heater O'Ring Gaskets (Single) Type of product: Heater or pump 'O' ring Gasket / seal Most common size reference: 1.5 inch Dimensions: Approx thickness: 5mm Diameter: 59mm (external) Commonly used with: Balboa 1.5 inch heater. Voyager Spa amongst others. Additional notes: For use with 1.5 inch heater assemblies.