Made from solid high density polypropylene blocks with 13 slanted channels (on a 10o angle), 1/16"(1.5mm) (W) x ⅜" (9mm) (D). It is made to hold 3x1" (75x25mm) slides during cleaning, draining excess immersion oil, and even drying. They are white in color and are chemically resistant. Available in 40 or 90 capacity (vertically held).