About 10 month ago the company came out with the new FD-UR. Like someone said, it has two teeth down and one up.
The FD-SR was always my biggest seller but the UR is slowly taking over. It does not have the burr like other blades and therefore cuts more straight. Great for beginners. Some have told me that it last longer as many other blades.
An other nice thing is that the blades have a little marking on one end, telling you that it is the top or the bottom of the blade, so you don't have to look any more how the teeth are facing.
FD Mike