Used to grind an ACME thread form tool.
Small flat is ground and measured by way of slots on edge of gauge.
Here it is ground for 10 threads per inch.
A little hand honing and it is good to go.
Tool bit is 5% cobalt high speed steel 3/16th.
ACME threads are used for making things move and clamping.
Like the rod on your garage door opener C clamps lead screws on lathes and milling machines.
Many other uses too.
Very old school.
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