I found this OB Unipart at a small outdoor flea market near Eddyville Kentucky. The insulator caught my eye because it had a sand blast (s-b) mark on the upper skirt and a recess embossed (r-e) on the lower skirt. Pictures were posted to the Help folder and Elton Gish sent me the following info. The dual marking are not common and from the pictures and measurements your insulator is a U-875, Ohio Brass, the first ever reported. Enjoy the pictures and special thanks to Elton and David.