MLA

McKay, Claude, 1890-1948. Hennacy, Ammon. Box 18, folder 572. 1946 Aug 5. https://collections.library.yale.edu/catalog/16189049.

APA, 6th edition

McKay, Claude, 1890-1948. (["Box 18, folder 572"])(1946 Aug 5)[Hennacy, Ammon]. https://collections.library.yale.edu/catalog/16189049.