255.
Can a clustered index be made up of more than one column
View Description
Please note: a TABLE or VIEW can only have one CLUSTERED INDEX at a time. Think about it. If you were going to index a table of contacts, you can’t sort by the first name and the last name at the same time. One ordering would undo the other! If you want to order by one column and then the other column you can use multiple columns in your CREATE INDEX statement.
CREATE CLUSTERED INDEX cix_contact__lastname_firstName
ON contact (lastname, firstName)
This would order everything like a phone book. by last name and then first name