Last year I installed a new tap assembly in the kitchen sink. It includes a spray nozzle. Everything was fine for several months when I noticed it was leaking underneath. I turned off the water, disconnected everything, ran new thread tape, and re-attached and re-tightened the connections. Still leaks. Now I talked to a plumber today who mentioned something about an o-ring.(I found the source of the leak: the fitting on the hose on the source end of the spray nozzle hose.) What size o-ring do I need to buy?