Below you can see what
2-inch by 2-inch mount slides look like
with different positive film formats.
(Also known as photo slide sizes or types.)

35mm Film Slide
2-inch x 2-inch Mount

35mm Half Frame Film Slide
2-inch x 2-inch Mount

Super 35mm Film Slide
2-inch x 2-inch Mount

110 Film Slide
2-inch x 2-inch Mount

126 Film Slide
2-inch x 2-inch Mount

127 Film Slide
2-inch x 2-inch Mount
You can view different
photo slide mount (frame) sizes HERE.