This lot has the first 6 tubes marked with P.P. or P.P. U.S.A. for Porcelain Products Inc. The 3rd tube actually has a upside down P in part of the one marking. The next three are marked U.S.A. and a No Name. I attribute these to Porcelain Products because the U.S.A. marking is the same as there's just marked under the lip of the head. What makes these special is that they were designed for areial wire to go through them. In the next posting you will see what I mean in the inner slots of the tubes. The last tube is half of a long split tube with No Name on it.