MLA

Koch, Frederick R. (Frederick Robinson). Music/Variations on a Theme by Hindemith: drafts. Box 307, folder 1649. n.d.. https://collections.library.yale.edu/catalog/2017238.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 307, folder 1649"])(n.d.)[Music/Variations on a Theme by Hindemith: drafts]. https://collections.library.yale.edu/catalog/2017238.