Acme Viewer for Stereo 3D Slides - vintage
Plastic Grab-Light (available light) Stereo Slide Viewer with Amazing Quality -yet reasonably priced. View all formats of stereo slides in 1-5/8" x 4" mounts, of any material (cardboard, plastic, metal, glass) in degrees of thickness. View Nimslo/Half Frame, Realist/American (5 perf); European (7 perf) in any mount: cardboard, aluminum, glass; RBT, and also view RBT Wide and Full Frame formats with only slight vignetting.
Viewer comes highly recommended by Wiley Coyote.