Binding a default to a user-defined datatype
Select the User-defined Datatypes folder.
Select a user-defined datatype, then choose File | Properties.
Select the Advanced Options tab.
Select a default from the Default list.
Optionally, select In Future Only. If you select In Future Only, the default is applied only to columns of this type added to a table after you bind the default. It does not apply to columns of this type currently in a table. If you do not select In Future Only, the default is applied to columns of this type currently in tables and columns of this type added later.