Kodak Ektagraphic Film Strip Adaptor, NIB!

Don't see many of these especially in this condition.   This item is in New condition in the original box.  From all appearances it has never been used.

These adaptors were intended for classroom use with an audio cassette program and the matching 35mm filmstrip.  The adaptor is simply put in the projector in place of the lens and the filmstrip is fed through the gate manually.  The lens is a Kodak Ektanar 3", f2.8.