I want to buy spur gears for my rolling mill, but I don't know the size terminology, like pitch, pitch diameter.

If you are talking about US Coins

1. 0.955 inches
2. The diameter is 0.955 inches (24.26 mm), and the width of 0.069 inches (1.75 mm). The coin has a 0.069-inch (1.75-mm) reeded (or milled) edge. Owing to the introduction of the clad quarter in 1965, it was occasionally called a "Johnson Sandwich" after Lyndon B. Johnson, the U.S. President at the t

whats the outside diameter of the gear?

If you can't measure it directly, take the nut with you to a hardware store and find a bolt that fits it. But you can easily measure the pitch with a decent ruler. Just count the number of threads in one inch. Count the threads from one peak to the next, So if the first peak lines up with zero on your ruler and the thirteenth peak is at one inch, this would be a 12 tpi (threads per inch) pitch. If you can measure the diameter of the threaded shaft, you will find that the actual diameter of the threaded part is just a little smaller than the nominal size. For instance, a 5/8 diameter thread might measure about 0.610 inches.
Good luck!

Quarter-sawing is a method of milling trees into lumber. Quarter-sawn lumber is highly sought after, particularly in certain species such as oak or maple, where look of the grain in the wood is accentuated by the method of cutting the tree. While rip-sawing is the most efficient (and common) method of milling, quarter-sawing is more difficult to cut but yields much more stable lumber. Because it is more difficult to cut and there is more waste, quarter-sawn lumber is considerably more expensive than rip-sawn material.
(taken from http://woodworking.about.com)

Not personally, but when I was looking tobuy one I saw some useful reviews on amazon. See this link http://www.amazon.com/Peugeot-PM25601-Olivier-Roellinger-Chocolate/dp/B0027H4WI0

It's5 and a quarter inches tall.

You could use a .004 shim stock spacer. I wouldn't worry about it as you are only milling and it should not have much impact!

Good luck, Jack

Replace the PCV valve, about $15, bet it fixes your problem.