Step 9 · Install Gasket and Locking Nut
Move back to the area below the shower. Slide the new rubber gasket up the threads of the drain body until it sits flush against the underside of the shower base. Follow this with the friction washer (a cardboard or plastic washer that helps the nut turn without grabbing the rubber gasket). Finally, thread on the large locking nut. Hand-tighten the nut as much as you can, then use channel-lock pliers to give it another quarter to half turn until it is snug. Do not overtighten.