The instructions say this fits 1 1/4" to 1 1/2" opening.  The rubber washer ( provided ) is 1 1/4 " in diameter this does not allow the nut to compress it against the underside of the sink.  Therefore, with the nut tight it wobbles in the opening.  I had to install a washer on the sink side and a larger rubber washer on the underside to get a tight fit.