Many show as Hassit in Castle Garden immigration records. My John Hassett was also of Brownstown, Co Westmeath, possibly. There is a possibility the surname was Hassen for John and possibly for Phelim. Still checking on that. The surname ambiguity is because of Gaelic translation.

In newly published parish records the surname is spelled Hassan, Hassen, Hafsen (f=ss), Hassad, and Hassett. The Clonmellon, County Westmeath parish records include a fair amount of other individuals with this surname, men and maiden names of women.

http://registers.nli.ie/registers/