32 CFR 1630.44: Class 4-F: Registrant not acceptable for military service.

In Class 4-F shall be placed any registrant who is found by the Secretary of Defense, under applicable physical, mental or administrative standards, to be not acceptable for service in the Armed Forces; except that no such registrant whose further examination or re-examination is determined by the Secretary of Defense to be justified shall be placed in Class 4-F until such further examination has been accomplished and such registrant continues to be found not acceptable for military service.