Lufkin Round Screw Thread Calculator 1935
This is a very nice clean Screw Thread calculator copyright in 1935 by "THE LUFKIN RULE CO. SAGINAW MICH. U.S.A. COPYRIGHT 1935 L.R.CO." The calculator is two piece, the top section spins, for finding sizes of tap drills for NC and NF, also NPT on the back side, & decimal equivalents for fractions. They both are printed on a cardboard, or heavy paper. The calculator has a brass center pivot in good condition. Although these were printed until the 1950's era, we believe this one to be from the 1930's as the newer type has a clear coating over the cardboard, this one doesn't. There is a few pencil lines on the front face in the pcitures, those have been removed, so the only issue to report with this calculator is minor age toning/darkening and a few areas of minor edge dings. It measures about 3.3" in diameter. It's in very good shape!
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