The Vivitar S-100 Rotary Slide Tray is designed to hold up to 100 2x2 slides for use with slide projectors. This rotary tray features a compact design and is compatible with various slide projector brands such as GAF, Hanimex, Minolta, Keystone, and Sawyers. With its rotary feature, this tray allows for easy and convenient switching between different slide sets, making it a practical and efficient tool for film photography and slide presentations.