If the union on your heater doesn't thread on far enough to seal against the gasket properly, the Spacer Gasket can be used to act as a buffer to fill in the extra space behind the heater's lip.
If the union on your heater doesn't thread on far enough to seal against the gasket properly, the Spacer Gasket can be used to act as a buffer to fill in the extra space behind the heater's lip.