A tooth is over the center, that is, the end edge is beyond the center position. When is the note to work, allow me to give an example. When the keyway milling cutter is utilized to mill the keyway, if there is no tooth over the center, there will be a high point in the middle of the milled slot, so the 2-blade keyway cutter is a pair of teeth. All over the center.
If the milling cutter is working with a circumferential tooth, then the end tooth is not important at the center. Generally speaking, when we produce the tool, the odd-numbered edge milling cutter has a tooth over center and an even-numbered edge milling cutter with a couple of teeth passing through the center.
2-blade cutter sometimes has a pair of centers, sometimes a tooth that passes through the center.