the TE gauge has nothing to do with locking lugs,
its simply inserted into the breach, and a reading is taken from the back edge of the receiver ring, the M1icon Garand tool is dog legged since the bold cant be removed from the rear,
the 1903. 1917 you remove the bolt, and insert the tool through the receiver, and take readings the same way.
the 1903 17 also have a measurement for reading a loose barrel as well.