Here is a cropped picture from a Graybar catalog page showing the Diamond Bridle Wire Insulator. It also shows the Diamond Bolt Expansion Co. Bridle screw eye insulator. I have two Diamond Bolt Expansion Co. catalogs but neither one show the Wire insulator. I have previous posts years ago showing the Diamond Bolt Expansion Co. insulators and related. Just type in my name in the search to see all my posts over the years. It has been stated the glass portion was made by Wheaton Glass Works Millville, N.J. which is in relation to Whitall Tatum Co.