Top has SNC inscribed on metal piece. Has a wheel attached. Bottom has DNS and is a Molded plastic piece that slides in the bottom track.
Casey from SWISCO responded:
April 22, 2020
Hello,
Take a look at our Acme 23-026 guide and 23-027 roller for the top and bottom of the door. Please let us know if you have any other questions about these parts. Thanks for posting!