Polished glass equilateral prisms. Equilateral because each edge of the end is the same length. Thus, as all you geometry students know, each of the angles is also the same, 60 degrees. These are school grade and are fine for decorative and demonstration. They do a nice job of refracting light to produce a nice rainbow-like spectrum, but are definitely not up to instrumentation standards. Sides range from 23-25mm and the missing dimension, length, is shown below.