3 9/16" x 4 1/4" square Anderson Band pot
Anderson Band pots are often preferred by paph and phrag growers because they offer great length for long roots, and a very open bottom to allow water to flow freely. Tuck a piece of mesh in the bottom to keep bark mixtures contained, or fill the bottom with sphagnum moss.
Measures 3 9/16" across the top, 3" across the bottom and 4.25" tall.
To keep medium in the pot, place a small bit of screen or mesh in the bottom. Clear plastic embroidery canvas also works really well in the bottom of these, and can be purchase online or at any craft store.