These are 6mm Plastic Alphabet Beads.  The letter or design appears on four sides of the bead and the hole size is a roomy 4mm.

Also known as letter beads, alphabet beads are perfect for personalizing your craft projects.  Alphabet Beads are often used with Pony Beads to create beaded bracelets, beaded necklaces, beaded crafts, and other kids craft projects.