I have what appears to be an unembossed glazed pinhole u-610A in cobalt blue. I would like to know the manufacturer. It is the middle insulator between four Canadian Porcelain (CP) cobalts, a u-2239, a u-2582, a u-? and a u-2421. All 5 appear to have the same cobalt glaze including glazed pinholes. Is this a CP product? Has anyone else seen one? Thanks, Mark.