42 CFR § 407.11 - Forms used to apply for enrollment under Medicare Part B.

§ 407.11 Forms used to apply for enrollment under Medicare Part B.

The following forms, available free of charge by mail from CMS, or at any Social Security branch or district office, are used to apply for enrollment under the supplementary medical insurance program.

CMS-4040 - Application for Enrollment in the Supplementary Medical Insurance Program. (This form is used for enrollment by individuals who are not eligible for monthly benefits or for hospital insurance.)
CMS-40-B - Application for Medical Insurance. (For general use by the SSA District Office in requesting medical insurance protection during the general enrollment period or during the initial enrollment period if the enrollee is not subject to automatic enrollment is SMI.)
CMS-40-D - Application for Enrollment in the Supplementary Medical Insurance Program. (This form is mailed to individuals who do not have current supplementary medical insurance because of prior refusals, voluntary withdrawal, or premium default from prior coverage. It is used during the annual general enrollment period.)
CMS-40-F - Application for Medical Insurance. (For use by beneficiaries residing outside the United States.)
CMS-18-F-5 - Application for Hospital Insurance Entitlement. (For use by individuals who are not eligible for retirement benefits under Title II of the Social Security Act or under the Railroad Retirement Act. This form may also be used for enrollment in the supplementary medical insurance program.)
As an alternative, the individual may request enrollment by answering the Part B enrollment questions on an application for monthly Social Security benefits, or by signing a simple statement of request, if he or she is eligible to enroll at that time.