Another one of the most common G, D, and T concepts that everyone in machining should know about is concentricity. The indicator can be used to check for concentricity on the machine, on fixtures, and on parts. Here Mr. C. checks concentricity on a valve part groove using the surface plate, v-Block, and his .0005" BestTest test indicator.
![](https://i.ytimg.com/vi/W3QuPAq5HI4/maxresdefault.jpg)