Here is a rare picture of a B & T (Brunt & Thompson) Porcelain Co. wall tube from a catalog page in 1900. Extremely rare marking on tubes especialy compaired to the Brunt porcelain Co. pieces by that company and General Porcelain Co. Elton has a G.P.Co. marked tube in his article. I have yet to find one even though I've seen several catalog pages advertising them. Since General Porcelain Co. purchased the G.F. Brunt company and continued to use the Brunt markings for how long?, is probably the reason why I can't find a G.P. Co. marked tube. I have a few marked G.P.Co. nail knobs and other electrical porcelain but no tubes. On the flip side you can find a lot of G.P.Co. marked cleats. Go figure.