Yes, Virginia, film photography isn't quite dead and "slides" - the 50 x 50mm cardboard-mounted things - are still around. Our Physics department has a number of slide-mounted diffraction gratings for optics activities. I designed a few different handy mounts for them. One fits snugly on a standard 1/2" diameter aluminum lab rod. The others are vertically mounted to optics stands. One fits a 1/2" diameter hole, the other is for 10mm.