https://www.irs.gov/pub/irs-pdf/f8919.pdf
"Purpose of form.
Use Form 8919 to figure and report your share of the uncollected social security and Medicare taxes due on your compensation if you were an employee but were treated as an independent contractor by your employer. By filing this form, your social security earnings will be credited to your social security record. See https://www.irs.gov/businesses/small-businesses-self-employed/independent-contractor-self-employed-o... for more information."
[ The 8919"-T" is just to indicate the first taxpayer listed on the tax return and the 8919"-S" indicates the second taxpayer listed (the spouse) ]