§ 4208(b) preliminary commitment

it is plain that as far as the sentence is concerned the original order entered under § 4208(b) is wholly tentative. That section merely provides that commitment of a defendant to the custody of the Attorney General 'shall be deemed to be for the maximum sentence,' but does not make that the final sentence. The whole point of using § 4208(b) is, in its own language, to get 'more detailed information as a basis for determining the sentence to be imposed * * *.' It is only after the Director of the Bureau of Prisons makes his report that the court makes its final decision as to what the sentence will be.

Defined by the Supreme Court in - United States v. Behrens, 375 U.S. 162 (1963).