I found these at the same location where I found those other two insulators I posted. The light brown insulator as no embossing but the dark brown ones read PP 1933 USA. I would appreciate any kind of information. Thanks!
These are called secondary service wireholders. They're most commonly used on an electrical service drop to a house, especially around the 1940s and later. They're still current items and you can buy them from electrical supply companies, like this one: http://www.hubbellpowersystems.com/pole-line/service/wireholders-screw/
They don't generate much interest among collectors. Most prefer pin type insulators.
The one marked PP is probably Porcelain Products Company which had plants in various locations around Ohio and West Virginia. I'm not knowledgeable enough to say for certain if the 1933 is a date or a model number.