This guage does just what it says, it measures the wear in the throat of the firearm. Typically this gauge is graduated from 0-10 each number roughly representing 1000 rounds of wear. For example a TE reading of 5, would roughly represents 5000 rounds through the chamber. Factors in addition the bullet wear can of course have an effect on this reading, but it is a good way to get a rough reading on barrel wear.

 

Muzzle erosion (ME gauge, muzzle gauge, etc)

 

This gauge is anouther self explanatory gauge, and it measures the wear at the muzzle of the firearm. These gauges typiclly come graduated from 0-10 also, with a few only doing 0-5.  The number represent the same wear as the TE gauge 1 for every 1000 rounds. like the TE gauge above this is a rough reading. Many factors can effect this reading, inparticular a rifle that fired granades with have an extreamlly high ME rating.

 

Field gauge (field, headspace, etc)

 

Of the 3 headspace gauges a collector will only need the field gauge.  This gauge measures the maximum headspace of the rifle. You insert the gauge into the chamber on a stripped bolt as described in the headspacing section.  Your bolt should not close on this gauge if it does, the rifle is not safe to fire.

 

 

This is the most common of the 3 gauges and can be found at your local hardware store. The collector will use this tool to determine wear on various parts such as the Op Rod and Gas Cylinder, making sure they are not out of spec.