MLA

McKay, Claude, 1890-1948. Eastman, Max. Box 3, folder 67-71. 1926-50, n.d.. https://collections.library.yale.edu/catalog/10186854.

APA, 6th edition

McKay, Claude, 1890-1948. (["Box 3, folder 67-71"])(1926-50, n.d.)[Eastman, Max]. https://collections.library.yale.edu/catalog/10186854.