The Harmony Gasket for Round Orbix Hatch is the replacement interior lid gasket for the Harmony Oval Orbix Hatch lid. No tools required, fits into the groove on the underside of the hatch lid.
I bought this to replace the gasket on a used Tarpon 140 I got recently. The gasket was actually thinner that than the old one and about 1/4 inch shorter overall. Would have been nice for Harmony to give you a little extra so you could trim it to fit the hatch huh? You'd probably be better off going to your local Home Improvement store and getting some round foam window insulation to achieve a better seal. This was a disappointing purchase. Not ACK's fault. The Orbix hatch covers have been plagued with issues. We'll see if the new design solves the vexing problems of the past.