The adjusting screw can both squeeze the plates together or spread them apart.
The upper end of the screw has a 5/16-24 thread and the lower end has a 1/2-20 thread.
Both threads are right handed.
The indicator holding arm is made from one piece of steel and is split into two "leaves" by a saw cut.
The upper leaf is tapped with 5/16-24 and the lower leaf 1/2-20 threads.
The "leaves" cannot be disassembled.
The differential adjusting screw is made in two pieces. The 1/2-20 screw is drilled through with an approx. 1/4" dia. hole.
After assembly the two pieces of the adjusting screw are pinned together with a 1/16" diameter cross pin that can be seen in the photo.
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