For 2" heater unions, this flat gasket has a raised o-ring in the center.

2" connections are the most common heater size, and will work for most Gecko, Balboa, Hydroquip, Waterway, CTI (Correct-Tech) and other spa heaters.

The raised o-ring portion measures approximately 2-1/2" diameter, center to center on the raised o-ring.

The flat gasket portion measures approximately 2-1/8" inside diameter and 2-15/16" outside diameter.

2" heater union tailpieces are here.