The RootsWeb SSDI http://ssdi.genealogy.rootsweb.com/cgi-bin/ssdi.cgihttp://ssdi.genealogy.rootsweb.com/cgi-bin/ssdi.cgi has 3 Harry Casselberry entries. If one is your grandfather, you can put an electronic post-em on him for free. The SSA will sell you a copy of his SSN application for $27. It will have his parent's names. "Krank" looks a lot like a nick name or typo to me. Out of 68 million people on the SSDS, none have a given name of Krank. Did you mean to type "Hank"?
Dates help, too; depending on birth order and your age, your grandparent can be born 60 to 160 years ago.