31 CFR § 363.162 - Who may convert a definitive savings bond?
(a) Bond that is registered to the account owner. The following persons may convert a definitive savings bond of an eligible series to a book-entry bond to be held in the person's TreasuryDirect account:
(2) Either co-owner of a bond registered in the coowner form of registration; and
(b) Bond that is registered to someone other than the account owner. We will convert an eligible definitive savings bond submitted by an individual account owner who is not the registered owner of the savings bond. See the special rules in § 363.166.