“STARRETT” TOOLS CELLULOID DEVICE TO CALCULATE SCREW THREADS & TAP DRILLS.
2.5 x 4” with 1936 copyright and the earliest item we recall seeing with name of ad specialty/button maker N.G. Slater. Device had dial and cut-out window for use in determining: Size of Tap/Number of Threads Per Inch/ Size of Tap Drill. Additional charts on reverse. Very Fine.
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