The very first insulator I ever found myself was an arc-embossed Tatum 107. Not real sexy, but it drew my attention to them. In 46 years I have never seen the example on the left with the full embossing (including "CO") in clear. The example on right has the "CO" removed. According to Woodward, the latter was only made for about a year after Armstrong bought out Tatum in 1937, making them somewhat unusual. By comparison, I see them from time-to-time, where I have never seen the other before. Own the pair for $18 + postage.