MLA

Lewis, Sinclair, 1885-1951. Garland, Hamlin. Box 47, folder 505. undated. https://collections.library.yale.edu/catalog/17116542.

APA, 6th edition

Lewis, Sinclair, 1885-1951. (["Box 47, folder 505"])(undated)[Garland, Hamlin]. https://collections.library.yale.edu/catalog/17116542.