Lufkin Round Screw Thread Calculator 1935
This is a 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 with a clear coating on it. We note a few very small areas where the clear coating has peeled off, considered minor. 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 1940's. It measures about 3.3" in diameter. It's in great shape!