MLA

Saarinen, Eero, 1910-1961. SK sketches. Box 617. undated. https://collections.library.yale.edu/catalog/10021527.

APA, 6th edition

Saarinen, Eero, 1910-1961. (["Box 617"])(undated)[SK sketches]. https://collections.library.yale.edu/catalog/10021527.