Here is a photo of three CD 735 threadless hat insulators, that were donated to the NIA. The cobalt one on the left looks to be the same as the one posted and asked about recently. All three examples shown here appear to have been made in the same mold. Note the very flat base with square inner edge, with rough glass extending downward around the outside edge, much like an EC&M. This cobalt example has a few rusty red swirls in it as well.
These are almost certainly bogus.