Tournée Cut: Cooking Terms: RecipeTips.com
Phil is right.
"Competition" tourne have 7 sides. Turn of the century Russo-French cuisine, the most OCD of all, allowed for 5, 6 or 7. I don't remember what Escoffier said and I'm too lazy to go look. Most people, including me, find 8 easier. As Phil said, there's no set size, but it's very important to be consistent in a given service. I use the reference points on my knife to get consistent sizes.
The right way to START learning to make this cut is to hard boil a bunch of eggs, let them dry and cool, stick masking tape to the shells, and practice carving it off. Once you get terminally frustrated trying to make ovoid cuts, cut sticks of 3/4" square-cross section, the length of the distance between rivets on your knife (about 1-3/4"). Hold the edge of a small knife against one of the four long edge, move the stick so the knife carves a 45 deg angle, taking about 1/3 of each adjacent face. Turn the stick as you approach the end, so the cut trails towards the center. Take your time -- you'll become so bored the cut becomes automatic, at which point your technique and speed can improve -- slightly. I'm told you can come to actually enjoy it. I wouldn't know.
If the whole thing seems tedious and anal beyond belief, I understand you can buy frozen, turned carrots. But I have no idea from where you'd buy them.