What kind of beads are they?
"E" beads are glass seed beads that measure 5⁰ and 6⁰ (often written 5/0 and 6/0, or just called sizes 5 and 6). Unlike other seed beads, their circumference is not perfectly smooth and round. Like many seed beads, "E" beads are usually made in the Czech Republic.

Why are they called "E"?
The letter refers to the beads' shape. Their form resembles the flattened sides on a slice of bread; just as bread is cut from a loaf, "E" beads are cut from an elongated tube of glass. The slicer used in this process is shaped much like the letter "E," therefore creating slightly squared-off beads as it presses down on the tube.

What's that funny little zero?
That zero refers to the number of aughts, which is a unit used to indicate the size of small (seed) beads. The scale is inverted, so larger numbers of aughts correspond to smaller beads (i.e. the bigger the number, the smaller the bead). Size 6 would be 000000, but since that takes up too much room, it is abbreviated to 6/0. Historians say the aught unit originated from the number of  beads that comfortably could be strung onto 1 inch of cord. This theory does match closely with present sizes, as a strand of x beads of size x/0 occupies about 0.8 inches (20 mm) of cord. The word aught means "zero," and is a relatively recent corruption of the old English word naught, meaning "nothing." Reportedly, the phrase "a naught" (which means "zero") became falsely divided into "an aught."

So how big is an "E" bead in standard measurements?

• Size 5s are 3.8-4.8mm tall, 2-3mm thick and have a 1.3-1.8mm hole.
• Size 6s are 3.5-4.4mm tall, 2-3mm thick and have a 1.3-1.8mm hole.