This is a mandatory part to install the new sink hardware - one thing Wayfair needs to do is make sure the customer UNDERSTANDS if you are installing a NEW VANITY you must have the ROUGH IN DRAIN ASSEMBLY! My installer looked at me like I was crazy when we reviewed all the parts I had ordered prior to install. He said, " where is everything else?" so I had to delay the install and quickly order the additional parts... Lesson Learned!